LED light bulb with conductive sections and exposed wires

ABSTRACT

An LED light bulb, comprising: a lamp housing, a bulb base, connected with the lamp housing; a stem with a stand extending to the center of the lamp housing, disposed in the lamp housing; a single flexible LED filament, disposed in the lamp housing, the flexible LED filament comprising: a plurality of LED sections, each of the LED sections includes at least two LED chips that are electrically connected to each other by a wire; a plurality of conductive sections comprising a conductor, located between the adjacent two LED sections; a light coversion layer disposing on the LED chip and at least two sides of the conductive electrodes and exposing a portion of the conductive electrodes, the light coversion layer is composed of at least one top layer and at least one base layer, where the top layer only cover the LED chip and the conductor completely and exposes a portion of the wire.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 16/479,220 filed on 2019 Jul. 19, which claims priority to ChinesePatent Applications No. 201711434993.3 filed on 2017 Dec. 26; No.201711477767.3 filed on 2017 Dec. 29; No. 201810031786.1 filed on 2018Jan. 12; No. 201810065369.9 filed on 2018 Jan. 23; No. 201810343825.1filed on 2018 Apr. 17; No. 201810344630.9 filed on 2018 Apr. 17; No.201810501350.4 filed on 2018 May 23; No. 201810498980.0 filed on 2018May 23; No. 201810573314.9 filed on 2018 Jun. 6; No. 201810836433.9filed on 2018 Jul. 26; No. 201810943054.X filed on 2018 Aug. 17; No.201811005536.7 filed on 2018 Aug. 30; No. 201811005145.5 filed on 2018Aug. 30; No. 201811079889.1 filed on 2018 Sep. 17; No. 201811277980.4filed on 2018 Oct. 30; No. 201811285657.1 filed on 2018 Oct. 31; No.201811378173.1 filed on 2018 Nov. 19; No. 201811378189.2 filed on 2018Nov. 19; No. 201811549205.X filed on 2018 Dec. 18, each of which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a lighting field, and moreparticularly to an LED light bulb with conductive sections and exposedwires.

RELATED ART

Incandescent bulbs have been widely used for homes or commerciallighting for decades. However, incandescent bulbs are generally withlower efficiency in terms of energy application, and about 90% of energyinput can be converted into a heat form to dissipate. In addition,because the incandescent bulb has a very limited lifespan (about 1,000hours), it needs to be frequently replaced. These traditionalincandescent bulbs are gradually replaced by other more efficientlighting devices, such as fluorescent lights, high-intensity dischargelamps, light-emitting diodes (LEDs) lights and the like. In theseelectric lamps, the LED light lamp attracts widespread attention in itslighting technology. The LED light lamp has the advantages of longlifespan, small in size, environmental protection and the like,therefore the application of the LED light lamp continuously grows.

In recent years, LED light bulbs with LED filaments have been providedon the market. At present, LED light bulbs using LED filaments asillumination sources still have the following problems to be improved.

Firstly, an LED hard filament is provided with a substrate (for example,a glass substrate) and a plurality of LED chips disposed on thesubstrate. However, the illumination appearance of the LED light bulbsrelies on multiple combinations of the LED hard filaments to produce thebetter illumination appearances. The illumination appearance of thesingle LED hard filament cannot meet the general needs in the market. Atraditional incandescent light bulb is provided with a tungstenfilament, the uniform light emitting can be generated due to the naturalbendable property of the tungsten filament. In contrast, the LED hardfilament is difficult to achieve such uniform illumination appearances.There are many reasons why LED hard filaments are difficult to achievethe uniform illumination appearance. In addition to the aforementionedlower bendable property, one of the reasons is that the substrate blocksthe light emitted by the LED chip, and furthermore the light generatedby the LED chip is displayed similar to a point light source whichcauses the light showing concentrated illumination and with poorillumination uniformity. In other words, a uniform distribution of thelight emitted from LED chip produces a uniform illumination appearanceof the LED filament. On the other hand, the light ray distributionsimilar to a point light source may results in uneven and concentratedillumination.

Secondly, there is one kind of LED soft filament, which is similar tothe structure of the above-mentioned LED hard filament and is employed aflexible printed circuit substrate (hereinafter referred to FPC) insteadof the glass substrate to enable the LED filament having a certaindegree of bending. However, by utilizing the LED soft filament made ofthe FPC, the FPC has a thermal expansion coefficient different from thatof the silicon gel coated covering the LED soft filament, and thelong-term use causes the displacement or even degumming of the LEDchips. Moreover, the FPC may not beneficial to flexible adjustment ofthe process conditions and the like. Besides, during bending the LEDsoft filament it has a challenge in the stability of the metal wirebonded between LED chips. When the arrangement of the LED chips in theLED soft filament is dense, if the adjacent LED chips are connected bymeans of metal wire bonding, it is easy to cause the stress to beconcentrated on a specific part of the LED soft filament when the LEDsoft filament is bent, thereby the metal wire bonding between the LEDchips are damaged and even broken.

In addition, the LED filament is generally disposed inside the LED lightbulb, and in order to present the aesthetic appearance and also to makethe illumination of the LED filament more uniform and widespread, theLED filament is bent to exhibit a plurality of curves. Since the LEDchips are arranged in the LED filaments, and the LED chips arerelatively hard objects, it is difficult for the LED filaments to bebent into a desired shape. Moreover, the LED filament is also prone tocracks due to stress concentration during bending.

In order to increase the aesthetic appearance and make the illuminationappearance more uniform, an LED light bulb has a plurality of LEDfilaments, which are disposed with different placement or angles.However, since the plurality of LED filaments need to be installed in asingle LED light bulb, and these LED filaments need to be fixedindividually, the assembly process will be more complicated and theproduction cost will be increased.

In addition, since the driving requirements for lighting the LEDfilament are substantially different from for lighting the conventionaltungsten filament lamp. Therefore, for LED light bulbs, how to design apower supply circuitry with a stable current to reduce the ripplephenomenon of the LED filament in an acceptable level so that the userdoes not feel the flicker is one of the design considerations. Besides,under the space constraints and the premises of achieving the requiredlight efficiency and the driving requirements, how to design a powersupply circuitry with the structure simply enough to embed into thespace of the lamp head is also a focus of attention.

Patent No. CN202252991U discloses the light lamp employing with aflexible PCB board instead of the aluminum heat dissipation component toimprove heat dissipation. Wherein, the phosphor is coated on the upperand lower sides of the LED chip or on the periphery thereof, and the LEDchip is fixed on the flexible PCB board and sealed by an insulatingadhesive. The insulating adhesive is epoxy resin, and the electrodes ofthe LED chip are connected to the circuitry on the flexible PCB board bygold wires. The flexible PCB board is transparent or translucent, andthe flexible PCB board is made by printing the circuitry on a polyimideor polyester film substrate. Patent No. CN105161608A discloses an LEDfilament light-emitting strip and a preparation method thereof. Whereinthe LED chips are disposed without overlapped, and the light-emittingsurfaces of the LED chips are correspondingly arranged, so that thelight emitting uniformity and heat dissipation is improved accordingly.Patent No. CN103939758A discloses that a transparent and thermallyconductive heat dissipation layer is formed between the interface of thecarrier and the LED chip for heat exchange with the LED chip. Accordingto the aforementioned patents, which respectively use a PCB board,adjust the chips arrangement or form a heat dissipation layer, the heatdissipation of the filament of the lamp can be improved to a certainextent correspondingly; however, the heat is easy to accumulate due tothe low efficiency in heat dissipation. The last one, Publication No.CN204289439U discloses an LED filament with omni-directional lightcomprising a substrate mixed with phosphors, at least one electrodedisposed on the substrate, at least one LED chip mounted on thesubstrate, and the encapsulant coated on the LED chip. The substrateformed by the silicone resin contained with phosphors eliminates thecost of glass or sapphire as a substrate, and the LED filament equippingwith this kind of substrate avoids the influence of glass or sapphire onthe light emitting of the LED chip. The 360-degree light emitting isrealized, and the illumination uniformity and the light efficiency aregreatly improved. However, due to the fact that the substrate is formedby silicon resin, the defect of poor heat resistance is a disadvantage.

SUMMARY

It is noted that the present disclosure includes one or more inventivesolutions currently claimed or not claimed, and in order to avoidconfusion between the illustration of these embodiments in thespecification, a number of possible inventive aspects herein may becollectively referred to “present/the invention.”

A number of embodiments are described herein with respect to “theinvention.” However, the word “the invention” is used merely to describecertain embodiments disclosed in this specification, whether or not inthe claims, is not a complete description of all possible embodiments.Some embodiments of various features or aspects described below as “theinvention” may be combined in various ways to form an LED light bulb ora portion thereof.

In accordance with another embodiment of the present invention, an LEDfilament comprises at least one LED section, a conductive section, atleast two conductive electrodes and a light conversion layer. Theconductive section is located between two adjacent LED sections. The twoconductive electrodes are disposed on the LED filament correspondinglyand electrically connected to each of the LED sections. The adjacent twoLED sections are electrically connected to each other through theconductive section. Each of the LED sections includes at least two LEDchips, and the LED chips are electrically connected to each other by atleast one wire. The light conversion layer covers the LED sections, theconductive sections and the conductive electrodes, and a part of each ofthe two electrodes is exposed respectively.

In accordance with an embodiment of the present invention, theconductive section includes a conductor connecting with the LED section,and the length of the wire connecting between the LED chips is less thanthe length of the conductor.

In accordance with an embodiment of the present invention, the lightconversion layer includes at least one top layer and one base layer.

In accordance with another embodiment of the present invention, an LEDfilament comprises at least one LED section, a conductive section, atleast two conductive electrodes and a light conversion layer. Theconductive section is located between two adjacent LED sections. The twoconductive electrodes are electrically connected to the LED sections.The adjacent two LED sections are electrically connected to each otherthrough the conductive section. Each of the conductive sections iselectrically connected to the LED section by at least one wire.

In accordance with an embodiment of the present invention, each of theLED sections includes at least two LED chips, and the LED chips areelectrically connected to each other by the wire.

In accordance with another embodiment of the present invention providesa composition which is suitable for use as a filament substrate or alight conversion layer, wherein the composition comprises at least amain material, a modifier and an additive. The main material is anorganosilicon-modified polyimide; the modifier is a thermal curingagent; and the additives comprise microparticles added into the mainmaterial, which may comprise phosphor particles, heat dispersingparticles. The additive also comprises a coupling agent.

The present disclosure provides a composition which is suitable for useas a filament substrate or a light-conversion layer, wherein the mainmaterial in the composition is an organosilicon-modified polyimide, i.e.a polyimide comprising a siloxane moiety, wherein theorganosilicon-modified polyimide comprises a repeating unit representedby general Formula (I):

In general Formula (I), Ar¹ is a tetra-valent organic group having abenzene ring or an alicyclic hydrocarbon structure, Ar² is a di-valentorganic group, R is each independently methyl or phenyl, and n is 1˜5.

According to an embodiment of the present disclosure, Ar¹ is atetra-valent organic group having a monocyclic alicyclic hydrocarbonstructure or a bridged-ring alicyclic hydrocarbon structure.

According to another embodiment of the present disclosure, Ar² is adi-valent organic group having a monocyclic alicyclic hydrocarbonstructure.

It is another object of the claimed invention to provide an LED lightbulb, an LED light bulb includes a lamp housing, a lamp cap, twoconductive brackets, a stem, and an LED filament. The lamp cap iselectrically connected to the lamp housing, the two conductive bracketsare disposed in the lamp housing, the stem extends from the lamp capinto the lamp housing, and the LED filament comprises a plurality of LEDchips and two conductive electrodes. The LED chips are arranged in anarray along the extending direction of the LED filaments, and the twoconductive electrodes are respectively disposed at two ends of the LEDfilament and electrically connected to the LED chips, and the twoconductive electrodes are respectively electrically connected to twoconductive brackets. Wherein the LED filament is curled to satisfysymmetry characteristics in which: while a top view of the LED lightbulb is presented in two dimensional coordinate system defining fourquadrants with a X-axis crossing the stem, an Y-axis crossing the stem,and an origin, a brightness presented by a portion of the LED filamentin the first quadrant in the top view is symmetric to a brightnesspresented by a portion of the LED filament in the second quadrant in thetop view with respect to the Y-axis and/or is symmetric to a brightnesspresented by a portion of the LED filament in the third quadrant in thetop view with respect to the origin; and while a side view of the LEDlight bulb is presented in two dimensional coordinate system definingfour quadrants with a Y′-axis aligned with the stem, an X′-axis crossingthe Y′-axis, and an origin, a brightness presented by a portion of theLED filament in the first quadrant in the side view is symmetric to abrightness presented by a portion of the LED filament in the secondquadrant in the side view with respect to the Y′-axis.

In accordance with an embodiment of the present invention, an LED lightbulb includes a lamp housing, a lamp caps, two conductive brackets, astem and an LED filament. Wherein, the lamp cap is electricallyconnected to the lamp housing, the two conductive brackets are disposedin the lamp housing, and the stem extends from the lamp cap into thelamp housing. Moreover, the LED filament comprises a plurality of LEDchips and two conductive electrodes. The LED chips are arranged in anarray along the extending direction of the LED filaments, and the twoconductive electrodes are respectively disposed at two ends of the LEDfilament and connected to the LED chips, and the two conductiveelectrodes are respectively connected two conductive brackets. Whereinthe LED filament is curled to satisfy symmetry while a top view of theLED light bulb is presented in two dimensional coordinate systemdefining four quadrants with a X-axis crossing the stem, an Y-axiscrossing the stem, and an origin, a structure of a portion of the LEDfilament in the first quadrant in the top view is symmetric to astructure of a portion of the LED filament in the second quadrant in thetop view with respect to the Y-axis and/or is symmetric to a structureof a portion of the LED filament in the third quadrant in the top viewwith respect to the origin; and while a side view of the LED light bulbis presented in two dimensional coordinate system defining fourquadrants with a Y′-axis aligned with the stem, an X′-axis crossing theY′-axis, and an origin, a structure of a portion of the LED filament inthe first quadrant in the side view is symmetric to a structure of aportion of the LED filament in the second quadrant in the side view withrespect to the Y′-axis.

In accordance with an embodiment of the present invention, an LED lightbulb includes a lamp housing, a lamp caps, two conductive brackets,stems and LED filaments. Wherein, the lamp cap is electrically connectedto the lamp housing, the two conductive brackets are disposed in thelamp housing, and the stem extends from the lamp cap into the lamphousing. Moreover, the LED filament comprises a plurality of LED chipsand two conductive electrodes. The LED chips are arranged in an arrayalong the extending direction of the LED filaments, and the twoconductive electrodes are respectively disposed at two ends of the LEDfilament and connected to the LED chips, and the two conductiveelectrodes are respectively connected two conductive brackets. Whereinthe LED filament is curled to satisfy symmetry while a top view of theLED light bulb is presented in two dimensional coordinate systemdefining four quadrants with a X-axis crossing the stem, an Y-axiscrossing the stem, and an origin, a length of a portion of the LEDfilament in the first quadrant in the top view is substantially equal tothat of a portion of the LED filament in the second quadrant in the topview and/or is substantially equal to that of a portion of the LEDfilament in the third quadrant in the top view; and while a side view ofthe LED light bulb is presented in two dimensional coordinate systemdefining four quadrants with a Y′-axis aligned with the stem, an X′-axiscrossing the Y′-axis, and an origin, a length of a portion of the LEDfilament in the first quadrant in the side view is substantially equalto that of a portion of the LED filament in the second quadrant in theside view.

In accordance with an embodiment of the present invention, a perspectivediagram of the light emission spectrum of an LED light bulb is provided.The LED light bulb may be any LED light bulb disclosed in the previousembodiments, the spectral distribution of the LED light bulb is mainlybetween the wavelength range of about 400 nm to 800 nm. Moreover, thereare three peak wavelengths P1, P2, P3 in wavelength ranges correspondingto the light emitted by the LED light bulb. The wavelength of the peakvalue P1 is between about 430 nm and 480 nm, the wavelength of the peakvalue P2 is between about 580 nm and 620 nm, and the wavelength of thepeak value peak P3 is between about 680 nm and 750 nm. The lightintensity of the peak P1 is less than that of the peak P2, and the lightintensity of the peak P2 is less than the light intensity of the peakP3.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more readily apparent to thoseordinarily skilled in the art after reviewing the following detaileddescription and accompanying drawings, in which:

FIG. 1A is a cross sectional view of an LED filament in accordance withan embodiment of the present invention;

FIG. 1B is a top view of the conductor of an LED filament in accordancewith an embodiment of the present invention;

FIG. 1C is a top view of the conductor of an LED filament in accordancewith an embodiment of the present invention;

FIG. 1D is a cross sectional view of the conductor of an LED filament inaccordance with an embodiment of the present invention;

FIGS. 1E to 1I are bottom views of various designs of the conductor ofan LED filament in accordance with the present invention;

FIGS. 1J to 1M are schematic views showing an LED filament withattaching strength being enhanced in accordance with the presentinvention, wherein FIG. 1J is a perspective view of a conductor, FIG. 1Kis a perspective view showing a base layer, a conductor and a top layer,and FIGS. 1L and 1M are cross sectional views along a line E1-E2 in FIG.1K for different structures;

FIG. 1N is a cross sectional view of the conductor of an LED filament inaccordance with an embodiment of the present invention;

FIG. 1O is a schematic view showing the bent state of the LED filamentof FIG. 1A in accordance with an embodiment of the present invention;

FIG. 2 is a schematic view showing the interfaces passing through by thelight emitted by the LED chip in accordance with the present invention;

FIG. 3A is a schematic structural view showing an embodiment of alayered structure of an LED filament in accordance with the presentinvention;

FIG. 3B is a schematic structural view of an LED chip bonding wire of anembodiment in accordance with the present invention;

FIG. 4 shows the TMA analysis of the polyimide before and after addingthe thermal curing agent;

FIG. 5 shows the particle size distributions of the heat dispersingparticles with different specifications;

FIG. 6A shows the SEM image of an organosilicon-modified polyimide resincomposition composite film (substrate);

FIG. 6B shows the cross-sectional scheme of an organosilicon-modifiedpolyimide resin composition composite film (substrate) according to anembodiment of the present invention;

FIG. 6C shows the cross-sectional scheme of an organosilicon-modifiedpolyimide resin composition composite film (substrate) according toanother embodiment of the present disclosure;

FIG. 7A illustrates a perspective view of an LED light bulb according tothe third embodiment of the instant disclosure;

FIG. 7B illustrates an enlarged cross-sectional view of the dashed-linecircle of FIG. 7A;

FIG. 7C is a projection of a top view of an LED filament of the LEDlight bulb of FIG. 7A;

FIG. 8A is a perspective view of an LED light bulb according to anembodiment of the present invention;

FIG. 8B is a front view of an LED light bulb of FIG. 8A;

FIG. 8C is a top view of the LED light bulb of FIG. 8A;

FIG. 8D is the LED filament shown in FIG. 8B presented in twodimensional coordinate system defining four quadrants;

FIG. 8E is the LED filament shown in FIG. 8C presented in twodimensional coordinate system defining four quadrants;

FIGS. 9A to 9D are respectively a perspective view, a side view, anotherside view and a top view of an LED light bulb in accordance with anembodiment of the present invention;

FIG. 10 is a schematic view showing the light emission spectrum of anLED light bulb in accordance with an embodiment of the presentinvention;

FIG. 11 is a schematic view showing the light emission spectrum of anLED light bulb in accordance with another embodiment of the presentinvention;

FIGS. 12A to 12C are schematic circuit diagrams of an LED filament inaccordance with an embodiment of the present invention;

DETAILED DESCRIPTION

The present disclosure provides a novel LED filament and its applicationthe LED light bulb. The present disclosure will now be described in thefollowing embodiments with reference to the drawings. The followingdescriptions of various implementations are presented herein for purposeof illustration and giving examples only. This invention is not intendedto be exhaustive or to be limited to the precise form disclosed. Theseexample embodiments are just that—examples—and many implementations andvariations are possible that do not require the details provided herein.It should also be emphasized that the disclosure provides details ofalternative examples, but such listing of alternatives is notexhaustive. Furthermore, any consistency of detail between variousexamples should not be interpreted as requiring such detail—it isimpracticable to list every possible variation for every featuredescribed herein. The language of the claims should be referenced indetermining the requirements of the invention.

In the drawings, the size and relative sizes of components may beexaggerated for clarity. Like numbers refer to like elements throughout.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items and may beabbreviated as “/”.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers, or steps, these elements, components, regions, layers, and/orsteps should not be limited by these terms. Unless the context indicatesotherwise, these terms are only used to distinguish one element,component, region, layer, or step from another element, component,region, or step, for example as a naming convention. Thus, a firstelement, component, region, layer, or step discussed below in onesection of the specification could be termed a second element,component, region, layer, or step in another section of thespecification or in the claims without departing from the teachings ofthe present invention. In addition, in certain cases, even if a term isnot described using “first,” “second,” etc., in the specification, itmay still be referred to as “first” or “second” in a claim in order todistinguish different claimed elements from each other.

It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

It will be understood that when an element is referred to as being“connected” or “coupled” to or “on” another element, it can be directlyconnected or coupled to or on the other element or intervening elementsmay be present. In contrast, when an element is referred to as being“directly connected” or “directly coupled,” or “immediately connected”or “immediately coupled” to another element, there are no interveningelements present. Other words used to describe the relationship betweenelements should be interpreted in a like fashion (e.g., “between” versus“directly between,” “adjacent” versus “directly adjacent,” etc.).However, the term “contact,” as used herein refers to a directconnection (i.e., touching) unless the context indicates otherwise.

Embodiments described herein will be described referring to plan viewsand/or cross-sectional views by way of ideal schematic views.Accordingly, the exemplary views may be modified depending onmanufacturing technologies and/or tolerances. Therefore, the disclosedembodiments are not limited to those shown in the views, but includemodifications in configuration formed on the basis of manufacturingprocesses. Therefore, regions exemplified in figures may have schematicproperties, and shapes of regions shown in figures may exemplifyspecific shapes of regions of elements to which aspects of the inventionare not limited.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the figures. It will be understood thatthe spatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

Terms such as “same,” “equal,” “planar,” or “coplanar,” as used hereinwhen referring to orientation, layout, location, position, shapes,sizes, amounts, or other measures do not necessarily mean an exactlyidentical orientation, layout, location, position, shape, size, amount,or other measure, but are intended to encompass nearly identicalorientation, layout, location, position, shapes, sizes, amounts, orother measures within acceptable variations that may occur, for example,due to manufacturing processes. The term “substantially” may be usedherein to emphasize this meaning, unless the context or other statementsindicate otherwise. For example, items described as “substantially thesame,” “substantially equal,” or “substantially planar,” may be exactlythe same, equal, or planar, or may be the same, equal, or planar withinacceptable variations that may occur, for example, due to manufacturingprocesses.

Terms such as “about” or “approximately” may reflect sizes,orientations, or layouts that vary only in a small relative manner,and/or in a way that does not significantly alter the operation,functionality, or structure of certain elements. For example, a rangefrom “about 0.1 to about 1” may encompass a range such as a 0%-5%deviation around 0.1 and a 0% to 5% deviation around 1, especially ifsuch deviation maintains the same effect as the listed range.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present invention belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent application, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

The LED chip units or named with the LED section may be composed of asingle LED chip, or two LED chips. Of course, it may also includemultiple LED chips, that is, equal to or greater than three LED chips.

The connection mode between the conductor in the conductive section andthe light conversion layer is described as follows. Referring to FIG.1A, in the LED filament structure shown in FIG. 1A, the LED filament 400has a light conversion layer 420, the LED sections 402, 404, theconductive electrodes 410, 412, and at least one conductive section 430.The conductive section 430 is located between adjacent LED sections 402and 404. The LED sections 402 and 404 include at least two LED chips 442electrically connected to each other through the wires 440. In thepresent embodiment, the conductive section 430 includes a conductor 430a. The conductive section 430 and the LED sections 402, 404 areelectrically connected by wires 450, that is, two LED chips respectivelylocated in the adjacent two LED sections 402, 404 and closest to theconductive section 430 are electrically connected to each other throughthe wires 450 connecting with the conductor 430 a in the conductivesection 430. The length of the conductive section 430 is greater thanthe distance between two adjacent LED chips in one single LED sections402, 404, and the length of the wire 440 is less than the length of theconductor 430 a. The light conversion layer 420 is disposed on at leastone side of the LED chip 442 and the conductive electrode 410, 412, anda part of the two conductive electrodes is exposed from the lightconversion layer. The light conversion layer 420 includes at least a toplayer 420 a and a base layer 420 b. In the present embodiment, the LEDsections 402, 404, the conductive electrodes 410, 412, and theconductive section 430 are all attached to the base layer 420 b.

The conductor 430 a can be a copper foil or other electricallyconductive material, and the conductor 430 a has opening. The uppersurface of the conductor 430 a may further have a silver plating layer,and subsequently, the LED chip 442 may be attached to the base layer 420b by means of die bond paste or the like. Thereafter, a phosphor glue orphosphor film is applied to coat over the LED chip 442, the wires 440,450, and a portion of the conductive electrodes 410, 412 to form a lightconversion layer 420. The width or/and the length of the opening of theconductor 430 a are respectively larger than the width or/and the lengthof the LED chip 442 and defining the position of the LED chip 442. Atleast two of the six faces of the LED chip, generally five faces in thepresent embodiment, being covered by the phosphor glue. The wires 440,450 may be gold wires. In the present embodiment, the combination ofcopper foil 460 and the gold wire 440 provides a solid conductivestructure and also maintaining the flexibleness of the LED filament.Besides, the silver plating layer 461 has an effect of increasing lightreflection in addition to good electrical conductivity.

In an embodiment, the shape of the conductor may also result fromconsidering the gold wire connection or filament bending. For example,in one embodiment, a top view of conductor 430 a is shown in FIG. 1B,the conductor 430 a has a joint region 5068 and a transition region5067. The joint region 5068 is at the end of the conductor 430 a forbeing electrically connected with other components. In the presentembodiment, the conductor 430 a comprises two joint regions 5068, andthe transition region 5067 is located between two joint regions 5068 andfor connecting the two joint regions 5068. The width of the joint region5068 may be greater than that of the transition region 5067. Since thejoint region 5068 is used to serve as a pad for electrical contact, arelatively sufficient width is required. For example, if the width ofthe LED filament is W, the width of the joint region 5068 of theconductor 430 a can be between around ¼W and W. The joint region 5068can be multiple and the width thereof may be not consistent. Because thetransition region 5067 between the joint regions 5068 is not required toform any joint point, the width can be less than that of the jointregion 5068. For example, if the width of the LED filament is W, thewidth of the transition region 5067 can be between 1/10 W and ⅕ W, theconductor 430 a is easily to be bent along with the bending of thefilament due to the less width of the transition region 5067 of theconductor 430 a; therefore, the risk that a wire close to the conductormay be easily broken by stress of bending is lower.

In one embodiment, as shown in the top view of FIG. 1C, one of the LEDchips 442 constituting an LED filament is connected to the conductor 430a via the wire 450, wherein the conductor 430 a has two openings likenotch or rabbet with the quadrilateral shape symmetrically at the twoterminals of the conductor 430 a. Therefore, the LED chip disposing inthe opening has three sides opposite to the part of the conductor 430 a.Moreover, two terminals of the conductor 430 a being defined as thetransition region 5067 and the middle area between the terminals beingdefined as the joint region 5068 having a width Wc. Furthermore, eachtransition region 5067 of the conductor 430 a is divided into two stripswith the width Wt1 and Wt2 symmetrically aligned with the longitudinalcenterline of the conductor 430 a. Moreover, the sum of the widths ofthe two strips of the transition regions 5067, that is the width Wt1 andWt2, is less than the width of the joint region 5068 Wc. As shown inFIG. 1C, the sum of the widths Wt1, Wt2 of the two strips of thetransition regions 5067 is less than the width We of the joint region5068 in the direction perpendicular to the longitudinal of the LEDfilament, which can increase the mechanical strength between theconductor and the LED chip 442 of the LED filament and also to avoid thedamage of the wires 450 connecting the LED chips and the conductors. Inan embodiment, the length of the strip of the transition region mayextend to the LED section adjacent to the conductive section in thelongitudinal direction of the LED filament, thereby slow down the impactof the external force on the LED chip and improving product stability.In the present embodiment, the width We of the joint region 5068 isequal to the width of the base layer 420 b or the width of the LEDfilament, and the side of the LED chip 442 disposing in the openingwithout opposing the conductor 430 a is electrically connected to otherLED chips through the wire 440. The length of the wire 450 between theLED chip 442 and the conductor 430 a is shorter than the distancebetween any two LED chips in the LED section. For example, the length ofthe wire between the LED chip 442 and the conductor 430 a is shorterthan the distance between two adjacent LED chips in the LED section. Asa result, the risk of the LED filaments being broken caused by theelastic setback stress is also lower.

In one embodiment, the conductor 430 a in the LED filament has a contourconsisting of a joint region 5068 and four strip shaped transitionregions 5067 as shown in FIG. 1C. Further, the conductor 430 a can beillustrated with a left half portion and a right half portionsymmetrically aligned with the short axis centerline thereof such as aleft half portion or a right half portion of the bottom view shown inthe FIG. 1E, FIG. 1G, FIG. 1H and FIG. 1I. In other embodiments, theconductor 430 a may not having symmetric contour with respect to theshort axis centerline thereof, and the transition region 5067 forconnecting the joint regions 5068 may be any combination of thetransition regions 5067 shown in FIG. 1E, FIG. 1F, and FIGS. 1G, 1H, and1I. As shown in FIG. 1J, the conductor 430 a has at least one throughhole 506 p, and also referring to FIG. 1D and FIG. 1E. FIG. 1D is across sectional view of the conductor 430 a and the FIG. 1E is a bottomview shown a left half portion or a right half portion of the conductor430 a in the FIG. 1D. Wherein the base layer 420 b, for example thephosphor film, infiltrates the hole 506 p from one end, and optionallyselected to fill up to the other end of the hole 506 p. The phosphorfilm showed in FIG. 1D is not filled to the overflow through hole.Moreover, in the present embodiment, the upward surface of FIG. 1D isroughened so that the surface thereof has better thermal dissipationcapability. In other embodiments, the conductor 430 a may be locatedbetween the top layer 420 a and the base layer 420 b as shown in FIG.1L, the base layer 420 b has a beveled groove, and the through hole sizeof the conductor 430 a is smaller than the maximum size of the bevelgroove of the base layer 420 b. Therefore, when the phosphor film, thatis, the material of the top layer 420 a, overlies the conductor 430 aand fills the through hole, the phosphor film in the bevel groovepartially contacts the area under the conductor 430 a. As shown in FIG.1L, FIG. 1L is a cross sectional view taken along the line E1-E2 of FIG.1K. The phosphor glue used to form the top layer 420 a is filled intothe through hole 506 p of the conductor 430 a and then further filledinto the beveled groove of the base layer 420 a. In another embodiment,as shown in FIG. 1M, the phosphor film used to form the base layer 420 bis filled into the through hole 506 p of the conductor 430 a and thenfurther filled till contacting the surface of the top layer 420 a. Asshown in FIG. 1L and FIG. 1M, since the conductor 430 a is similarlyriveted by the top layer 420 a or the base layer 420 b in the axialdirection of the LED filament, the contact area between the conductor430 a and the top layer 420 a or the base layer 420 b is increased. Theincrease in the contact area that increases the bonding strength betweenthe conductor 430 a and the top layer 420 a or the base layer 420 b, andthe bendability of the conductive section is thereby improved.

FIGS. 1F, 1G, 1H and 1I are embodiments of the conductors 430 a havingthrough holes. The FIG. 1F is a partial bottom view of an LED filamentof an embodiment in which the conductor 430 a has only one transitionregions 5067 connected to the joint region 5068, whether the transitionregion 5067 or the joint region 5068 has a rectangular shape. The FIG.1F is a bottom view showing only a left half portion or a right halfportion of the conductor 430 a symmetrically aligned with the short axiscenterline thereof, and it is arranged with one strip shaped transitionregion 5067 connected to the joint region 5068. When the left halfportion is combined with the right half portion, the contour of theconductor 430 a may be any combination of the transition regions 5067and the joint regions 5068 shown in FIGS. 1E, 1F, 1G, 1H, and 1I. Takingthe central point of the LED chip 442 as the center, the shortestdistance from the center to the closest boundary of the joint region isset to r1, and the shortest distance from the center to the closestboundary of the transition region is set to r2. When the distance r1 isgreater than or equal to the distance r2, the broken risk of the LEDfilament caused by the elastic frustration stress can be reduced. TheFIG. 1F shows the case where r1 is greater than r2. In the case wherethe conductor 430 a is enclosed by the base layer 420 b, for example aphosphor film, referring to schematic diagram of FIG. 1F, the locationof the chip 442 is present with the dotted line due to the chip 442 isblocked by the base layer 420 b. From the bottom view, it is seen thatthe LED chip 442 overlaps the portion of the transition region 5067. Inother embodiments, the LED chip 442 does not overlap the portion of thetransition region 5067 in a bottom view. In other embodiments, theconductor comprises one joint region and two transition regions, onetransition region 5067 can be connected to the middle of the jointregion 5068, and another transition region can be connected to themiddle or one end of the joint region 5068, alternatively, anothertransition region 5067 can also be connected to the joint region 5068any position between the ends and the middle of the joint region 5068.When another transition region 5067 is connected to the middle jointregion 5068, the transition region 5067 and the joint region 5068 form ashape like a cross in the bottom view.

The difference between embodiments showing in the FIG. 1G and FIG. 1E isthe conductor 430 a in the embodiment of FIG. 1G having simply twotransition regions, each transition region 5067 of the conductor 430 ahaving two symmetrical contours symmetrically arranged about thelongitudinal axis of the LED filament and a portion of the contour is incontact with the joint region 5068. For example, each transition region5067 of the conductor 430 a is in a shape of trapezoid extending fromthe boundary of the joint region 5068 and the shorter trapezoidal sideaway from the joint region 5068. In other words, in the bottom view, thetransition region 5067 has a fixed end, that is the boundary of thejoint region 5068 connecting with the transition region 5067, whosewidth is equal to the length of the long side of the trapezoid or thewidth of the joint region 5068 and the base layer 420 b. In otherembodiments, the transition region 5067 whose width is gradually reducedfrom the fixed end to the other end may also be in a shape of triangularor semi-circular. The average width of the transition region 5067 isless than that of the joint region 5068. As shown in FIG. 1G, in thecase where the embedded conductor 430 a is enclosed by the base layer420 b (for example, a phosphor film), therefore the chip 442 is coveredby the base layer 420 b and from the bottom view the LED chip 442illustrated by the dashed line is overlapped with the transition region5067.

The difference between the FIG. 1H and FIG. 1F is the transition region5067 of FIG. 1H having two triangles symmetrical about the longitudinalaxis of the LED filament, one lateral of the triangle is aligned withthe outer side of the LED filament, and the other lateral is connectedwith the joint region 5068, and the oblique lateral of the triangle hasan end point intersecting with the joint region 5068 in the longitudinalaxis of the LED filament. The triangle being symmetrical designed in thetransition region 5067 may be an equilateral triangle, an acutetriangle, or an obtuse triangle, etc. In the present embodiment, the twooblique laterals of the two symmetrically triangles are intersected, butare not limited thereto. The distance between two oblique laterals inparallel with the short axial direction of the LED filament willgradually increase along the distance move away from a fixed end to theother end, that is, the two oblique laterals respectively intersectingwith the opposite sides of the base layer 420 b at the other end.Wherein the fixed end is the boundary of the joint region 5068connecting with the transition region 5067.

The embodiment of FIG. 1I is similar to FIG. 1H, the difference is theoblique lateral of the triangle of the transition region 5067 in FIG. 1Iis not a straight line but a stepped shape. In other embodiments, theoblique lateral of the triangle of the transition region 5067 can be inthe shape of curved, arched, or wavy. And all the structures describedbased on FIG. 1C to FIG. 1I also are able to be applied to the structureof electrode 410, 412.

Since the LED filament is placed inside the LED light bulb withundulating posture, the bending portion with a small radian may beweakened by the thermal stress due to thermal expansion caused by theheat generating from the LED light bulb. Therefore, the holes or notchescan be appropriately placed in the LED filament near the bending portionto mitigate this effect. In one embodiment, as shown in schematicdiagram FIG. 1N which the LED chip and the conductive electrode of theLED filament are omitted, the region between the D1 to D2 is apredetermined bending portion. The conductor 430 a is provided with aplurality of holes. Preferably, the size of the holes 468 are graduallyincreased from outer bending portion (showing as upper in the figure) tothe inner thereof (showing as), and the hole 468 is triangular in thecross sectional view of the present embodiment. When the LED filament isbent upward by the F direction, the LED filament is easier to bent dueto the plurality of holes 468 between the region from D1 to D2, and thehole 468 at the bending portion can buffer the thermal stress. Moreover,the deformation of the LED filament is followed the designed hole shapeand the bending angle.

FIG. 1O is a bending form of the LED filament shown in FIG. 1A of thepresent invention. In the related art, a plurality of LED filaments aregenerally connected by the conductive electrode to realize therequirement of curling the LED filament. Since the bending is occurredat the conductive electrode, the strength of that is less and easily tobe broken, further, the conductive electrode takes up some space to makethe light emitting area of the LED filament smaller. In the presentinvention, the conductive section 430 is a bent portion of the LEDfilament, and the rivet structure and the conductor reinforcement areformed by the conductor 430 a shown in FIGS. 1C to 1M, so that the wire450 connecting the LED chip 442 and the conductor 430 a is less likelyto be broken. In various embodiments, the conductors may be arranged ina configuration as shown in FIG. 1B or provided with an accommodatingspace on the conductor 430 a (e.g., the hole structure shown in FIG. 1N)to reduce the probability of the LED filament cracking during bending.The LED filament of the invention has the advantages of good bendabilityand high luminous efficiency.

When the LED filament is illuminated in an LED light bulb encapsulationwith the inert gas, as shown in FIG. 2, the light emitted by the LEDchip 442 passes through the interfaces A, B, C, D, E and F respectively,wherein the interface A is the interface between the p-GaN gate and thetop layer 420 a in the LED chip 442. The interface B is the interfacebetween the top layer 420 a and the inert gas, the interface C is theinterface between the substrate and the paste 450 (e.g., die bond paste)in the LED chip 442, the D interface is the interface between the paste450 and the base layer 420 b, the interface E is the interface betweenthe base layer 420 b and the inert gas, and the interface F is theinterface between the base layer 420 b and the top layer 420 a. Whenlight passes through the interfaces A, B, C, D, E and F respectively,the refractive index of the two substances in any interface is n1 and n2respectively, then |n1−n2|<1.0, preferably |n1−n2|<0.5, more preferably|n1−n2|<0.2. In one embodiment, the refractive index of two substancesin any one of the four interfaces of B, E, D and F is n1 and n2respectively, and then |n1−n2|<1.0, preferably |n1−n2|<0.5, Morepreferably |n1−n2|<0.2. In one embodiment, the refractive index of twosubstances in any interface of D and F two interfaces is n1 and n2respectively, then |n1−n2|<1.0, preferably |n1−n2I<0.5, preferably|n1−n2|<0.2. The absolute value of the difference in refractive index ofthe two substances in each interface is smaller, the light emittingefficiency is higher. For example, when the light emitted by the LEDchip 442 passes from the base layer 420 b to the top layer 420 a, theincident angle is θ1, the refraction angle is θ2, and the refractiveindex of the base layer 420 b is n1, and the refractive index of the toplayer 420 a is n2, according to the equation sin θ1/sin θ2=n2/n1, whenthe absolute value of the difference between n1 and n2 is smaller, theincident angle closer to the refraction angle, and then thelight-emitting efficiency of the LED filament is higher.

FIG. 3A is a schematic view showing an embodiment of a layered structureof the LED filament 400 of the present invention. The LED filament 400has a light conversion layer 420, two LED chip units 402, 404, twoconductive electrodes 410, 412, and a conductive section 430 forelectrically connecting adjacent two LED chip units 402, 404. Each ofthe LED chip units 402, 404 includes at least two LED chips 442 that areelectrically connected to each other by wires 440. In the presentembodiment, the conductive section 430 includes a conductor 430, and theconductive section 430 is electrically connected to the LED sections402, 404 through the wires 450. The shortest distance between the twoLED chips 442 located in the adjacent two LED chip units 402, 404 isgreater than the distance between adjacent two LED chips in the samechip unit 402/404. Moreover, the length of wire 440 is less than thelength of conductor 430 a. The light conversion layer 420 is disposed onthe LED chip 442 and at least two sides of the conductive electrodes410, 412. The light conversion layer 420 exposes a portion of theconductive electrodes 410, 412. The light conversion layer 420 maycomposed of at least one top layer 420 a and one base layer 420 b as theupper layer and the lower layer of the LED filament respectively. In thepresent embodiment, the LED chips 442 and the conductive electrodes 410,412 are sandwiched in between the top layer 420 a and the base layer 420b. When the wire bonding process of the face up chip is carried outalong the x direction, for example, the bonding wire and the bondingconductor are gold wires, the quality of the bonding wire is mainlydetermined by the stress at the five points A, B, C, D, and E as shownin FIG. 3B. The point A is the junction of the soldering pad 4401 andthe gold ball 4403, point B is the junction of the gold ball 4403 andthe gold wire 440, point C is between the two segments of the gold wire440, point D is the gold wire 440 and the two solder butted joints 4402,and the point E is between the two solder butted joints 4402 and thesurface of the chip 442. Because of point B is the first bending pointof the gold wire 440, and the gold wire 440 at the point D is thinner,thus gold wire 440 is frangible at points B and D. So that, for example,in the implementation of the structure of the LED filament 300 packageshowing in FIG. 3A, the top layer 420 a only needs to cover points B andD, and a portion of the gold wire 440 is exposed outside the lightconversion layer. If the one of the six faces of the LED chip 442farthest from the base layer 420 b is defined as the upper surface ofthe LED chip 442, the distance from the upper surface of the LED chip442 to the surface of the top layer 420 a is in a range of around 100 to200 μm.

The next part will describe the material of the filament of the presentinvention. The material suitable for manufacturing a filament substrateor a light-conversion layer for LED should have properties such asexcellent light transmission, good heat resistance, excellent thermalconductivity, appropriate refraction rate, excellent mechanicalproperties and good warpage resistance. All the above properties can beachieved by adjusting the type and the content of the main material, themodifier and the additive contained in the organosilicon-modifiedpolyimide composition. The present disclosure provides a filamentsubstrate or a light-conversion layer formed from a compositioncomprising an organosilicon-modified polyimide. The composition can meetthe requirements on the above properties. In addition, the type and thecontent of one or more of the main material, the modifier (thermalcuring agent) and the additive in the composition can be modified toadjust the properties of the filament substrate or the light-conversionlayer, so as to meet special environmental requirements. Themodification of each property is described herein below.

Adjustment of the Organosilicon-Modified Polyimide

The organosilicon-modified polyimide provided herein comprises arepeating unit represented by the following general Formula (I):

In general Formula (I), Ar¹ is a tetra-valent organic group. The organicgroup has a benzene ring or an alicyclic hydrocarbon structure. Thealicyclic hydrocarbon structure may be monocyclic alicyclic hydrocarbonstructure or a bridged-ring alicyclic hydrocarbon structure, which maybe a dicyclic alicyclic hydrocarbon structure or a tricyclic alicyclichydrocarbon structure. The organic group may also be a benzene ring oran alicyclic hydrocarbon structure comprising a functional group havingactive hydrogen, wherein the functional group having active hydrogen isone or more of hydroxyl, amino, carboxy, amido and mercapto.

Ar² is a di-valent organic group, which organic group may have forexample a monocyclic alicyclic hydrocarbon structure or a di-valentorganic group comprising a functional group having active hydrogen,wherein the functional group having active hydrogen is one or more ofhydroxyl, amino, carboxy, amido and mercapto.

R is each independently methyl or phenyl.

n is 1˜5, preferably 1, 2, 3 or 5.

The polymer of general Formula (I) has a number average molecular weightof 5000˜100000, preferably 10000˜60000, more preferably 20000˜40000. Thenumber average molecular weight is determined by gel permeationchromatography (GPC) and calculated based on a calibration curveobtained by using standard polystyrene. When the number averagemolecular weight is below 5000, a good mechanical property is hard to beobtained after curing, especially the elongation tends to decrease. Onthe other hand, when it exceeds 100000, the viscosity becomes too highand the resin is hard to be formed.

Ar¹ is a component derived from a dianhydride, which may be an aromaticanhydride or an aliphatic anhydride. The aromatic anhydride includes anaromatic anhydride comprising only a benzene ring, a fluorinatedaromatic anhydride, an aromatic anhydride comprising amido group, anaromatic anhydride comprising ester group, an aromatic anhydridecomprising ether group, an aromatic anhydride comprising sulfide group,an aromatic anhydride comprising sulfonyl group, and an aromaticanhydride comprising carbonyl group.

Examples of the aromatic anhydride comprising only a benzene ringinclude pyromellitic dianhydride (PMDA), 2,3,3′,4′-biphenyltetracarboxylic dianhydride (aBPDA), 3,3′,4,4′-biphenyl tetracarboxylicdianhydride (sBPDA), and4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA). Examples of thefluorinated aromatic anhydride include4,4′-(hexafluoroisopropylidene)diphthalic anhydride which is referred toas 6FDA. Examples of the aromatic anhydride comprising amido groupincludeN,N′-(5,5′-(perfluoropropane-2,2-diyl)bis(2-hydroxy-5,1-phenylene))bis(1,3-dioxo-1,3-dihydroisobenzofuran)-5-arboxamide)(6FAP-ATA), andN,N′-(9H-fluoren-9-ylidenedi-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxamide] (FDA-ATA). Examples of the aromatic anhydride comprisingester group include p-phenylene bis(trimellitate) dianhydride (TAHQ).Examples of the aromatic anhydride comprising ether group include4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA),4,4′-oxydiphthalic dianhydride (sODPA), 2,3,3′,4′-diphenyl ethertetracarboxylic dianhydride (aODPA), and4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride)(BPADA).Examples of the aromatic anhydride comprising sulfide group include4,4′-bis(phthalic anhydride)sulfide (TPDA). Examples of the aromaticanhydride comprising sulfonyl group include3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA). Examples ofthe aromatic anhydride comprising carbonyl group include3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA).

The alicyclic anhydride includes 1,2,4,5-cyclohexanetetracarboxylic aciddianhydride which is referred to as HPMDA, 1,2,3,4-butanetetracarboxylicdianhydride (BDA),tetrahydro-1H-5,9-methanopyrano[3,4-d]oxepine-1,3,6,8(4H)-tetrone (TCA),hexahydro-4,8-ethano-1H,3H-benzo[1,2-C:4,5-C′]difuran-1,3,5,7-tetrone(BODA), cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), and1,2,3,4-cyclopentanetetracarboxylic dianhydride (CpDA); or alicyclicanhydride comprising an olefin structure, such asbicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (COeDA).When an anhydride comprising ethynyl such as4,4′-(ethyne-1,2-diyl)diphthalic anhydride (EBPA) is used, themechanical strength of the light-conversion layer can be further ensuredby post-curing.

Considering the solubility, 4,4′-oxydiphthalic anhydride (sODPA),3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA),cyclobutanetetracarboxylic dianhydride (CBDA) and4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) arepreferred. The above dianhydride can be used alone or in combination.

Ar² is derived from diamine which may be an aromatic diamine or analiphatic diamine. The aromatic diamine includes an aromatic diaminecomprising only a benzene ring, a fluorinated aromatic diamine, anaromatic diamine comprising ester group, an aromatic diamine comprisingether group, an aromatic diamine comprising amido group, an aromaticdiamine comprising carbonyl group, an aromatic diamine comprisinghydroxyl group, an aromatic diamine comprising carboxy group, anaromatic diamine comprising sulfonyl group, and an aromatic diaminecomprising sulfide group.

The aromatic diamine comprising only a benzene ring includesm-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene,2,6-diamino-3,5-diethyltoluene, 3,3′-dimethylbiphenyl-4,4′-diamine9,9-bis(4-aminophenyl)fluorene (FDA),9,9-bis(4-amino-3-methylphenyl)fluorene, 2,2-bis(4-aminophenyl)propane,2,2-bis(3-methyl-4-aminophenyl)propane,4,4′-diamino-2,2′-dimethylbiphenyl(APB). The fluorinated aromaticdiamine includes 2,2′-bis(trifluoromethyl)benzidine (TFMB),2,2-bis(4-aminophenyl)hexafluoropropane (6FDAM),2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), and2,2-bis(3-amino-4-methylphenyl)hexafluoropropane (BIS-AF-AF). Thearomatic diamine comprising ester group includes[4-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate (ABHQ),bis(4-aminophenyl)terephthalate (BPTP), and 4-aminophenyl4-aminobenzoate (APAB). The aromatic diamine comprising ether groupincludes 2,2-bis[4-(4-aminophenoxy)phenyl]propane)(BAPP),2,2′-bis[4-(4-aminophenoxy)phenyl]propane (ET-BDM),2,7-bis(4-aminophenoxy)-naphthalene (ET-2,7-Na),1,3-bis(3-aminophenoxy)benzene (TPE-M),4,4′-[1,4-phenyldi(oxy)]bis[3-(trifluoromethyl)aniline] (p-6FAPB),3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether (ODA),1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(4-aminophenoxy)benzene(TPE-Q), and 4,4′-bis(4-aminophenoxy)biphenyl(BAPB). The aromaticdiamine comprising amido group includesN,N′-bis(4-aminophenyl)benzene-1,4-dicarboxamide (BPTPA), 3,4′-diaminobenzanilide (m-APABA), and 4,4′-diaminobenzanilide (DABA). The aromaticdiamine comprising carbonyl group includes 4,4′-diaminobenzophenone(4,4′-DABP), and bis(4-amino-3-carboxyphenyl) methane (or referred to as6,6′-diamino-3,3′-methylanediyl-dibenzoic acid). The aromatic diaminecomprising hydroxyl group includes 3,3′-dihydroxybenzidine (HAB), and2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP). The aromaticdiamine comprising carboxy group includes6,6′-diamino-3,3′-methylanediyl-dibenzoic acid (MBAA), and3,5-diaminobenzoic acid (DBA). The aromatic diamine comprising sulfonylgroup includes 3,3′-diaminodiphenyl sulfone (DDS),4,4′-diaminodiphenylsulfone, bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS) (or referred to as4,4′-bis(4-aminophenoxy)diphenylsulfone), and3,3′-diamino-4,4′-dihydroxydiphenyl sulfone (ABPS). The aromatic diaminecomprising sulfide group includes 4,4′-diaminodiphenyl sulfide.

The aliphatic diamine is a diamine which does not comprise any aromaticstructure (e.g., benzene ring). The aliphatic diamine includesmonocyclic alicyclic amine and straight chain aliphatic diamine, whereinthe straight chain aliphatic diamine include siloxane diamine, straightchain alkyl diamine and straight chain aliphatic diamine comprisingether group. The monocyclic alicyclic diamine includes4,4′-diaminodicyclohexylmethane (PACM), and3,3′-dimethyl-4,4-diaminodicyclohexylmethane (DMDC). The siloxanediamine (or referred to as amino-modified silicone) includesα,ω-(3-aminopropyl)polysiloxane (KF8010), X22-161A, X22-161B, NH15D, and1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (PAME). Thestraight chain alkyl diamine has 6˜12 carbon atoms, and is preferablyun-substituted straight chain alkyl diamine. The straight chainaliphatic diamine comprising ether group includes ethylene glycoldi(3-aminopropyl) ether.

The diamine can also be a diamine comprising fluorenyl group. Thefluorenyl group has a bulky free volume and rigid fused-ring structure,which renders the polyimide good heat resistance, thermal and oxidationstabilities, mechanical properties, optical transparency and goodsolubility in organic solvents. The diamine comprising fluorenyl group,such as 9,9-bis(3,5-difluoro-4-aminophenyl)fluorene, may be obtainedthrough a reaction between 9-fluorenone and 2,6-dichloroaniline. Thefluorinated diamine can be1,4-bis(3′-amino-5′-trifluoromethylphenoxy)biphenyl, which is ameta-substituted fluorine-containing diamine having a rigid biphenylstructure. The meta-substituted structure can hinder the charge flowalong the molecular chain and reduce the intermolecular conjugation,thereby reducing the absorption of visible lights. Using asymmetricdiamine or anhydride can increase to some extent the transparency of theorganosilicon-modified polyimide resin composition. The above diaminescan be used alone or in combination.

Examples of diamines having active hydrogen include diamines comprisinghydroxyl group, such as 3,3′-diamino-4,4′-dihydroxybiphenyl,4,4′-diamino-3,3′-dihydroxy-1,1′-biphenyl (or referred to as3,3′-dihydroxybenzidine) (HAB), 2,2-bis(3-amino-4-hydroxyphenyl)propane(BAP), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP),1,3-bis(3-hydro-4-aminophenoxy) benzene,1,4-bis(3-hydroxy-4-aminophenyl)benzene and3,3′-diamino-4,4′-dihydroxydiphenyl sulfone (ABPS). Examples of diaminescomprising carboxy group include 3,5-diaminobenzoic acid,bis(4-amino-3-carboxyphenyl)methane (or referred to as6,6′-diamino-3,3′-methylenedibenzoic acid),3,5-bis(4-aminophenoxy)benzoic acid, and1,3-bis(4-amino-2-carboxyphenoxy)benzene. Examples of diaminescomprising amino group include 4,4′-diaminobenzanilide (DABA),2-(4-aminophenyl)-5-aminobenzoimidazole, diethylenetriamine,3,3′-diaminodipropylamine, triethylenetetramine, andN,N′-bis(3-aminopropyl)ethylenediamine (or referred to asN,N-di(3-aminopropyl)ethylethylamine). Examples of diamines comprisingthiol group include 3,4-diaminobenzenethiol. The above diamines can beused alone or in combination.

The organosilicon-modified polyimide can be synthesized by well-knownsynthesis methods. For example, it can be prepared from a dianhydrideand a diamine which are dissolved in an organic solvent and subjected toimidation in the presence of a catalyst. Examples of the catalystinclude acetic anhydride/triethylamine, and valerolactone/pyridine.Preferably, removal of water produced in the azeotropic process in theimidation is promoted by using a dehydrant such as toluene.

Polyimide can also be obtained by carrying out an equilibrium reactionto give a poly (amic acid) which is heated to dehydrate. In otherembodiments, the polyimide backbone may have a small amount of amicacid. For example, the ratio of amic acid to imide in the polyimidemolecule may be 1˜3:100. Due to the interaction between amic acid andthe epoxy resin, the substrate has superior properties. In otherembodiments, a solid state material such as a thermal curing agent,inorganic heat dispersing particles and phosphor can also be added atthe state of poly (amic acid) to give the substrate. In addition,solubilized polyimide can also be obtained by direct heating anddehydration after mixing of alicylic anhydride and diamine. Suchsolubilized polyimide, as an adhesive material, has a good lighttransmittance. In addition, it is liquid state per se; therefore, othersolid materials (such as the inorganic heat dispersing particles and thephosphor) can be dispersed in the adhesive material more sufficiently.

In one embodiment for preparing the organosilicon-modified polyimide,the organosilicon-modified polyimide can be produced by dissolving thepolyimide obtained by heating and dehydration after mixing a diamine andan anhydride and a siloxane diamine in a solvent. In another embodiment,the amidic acid, before converting to polyimide, is reacted with thesiloxane diamine.

In addition, the polyimide compound may be obtained by dehydration andring-closing and condensation polymerization from an anhydride and adiamine, such as an anhydride and a diamine in a molar ratio of 1:1. Inone embodiment, 200 micromole (mmol) of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 20 micromole (mmol) of2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 50 micromole(mmol) of 2,2′-di(trifluoromethyl)diaminobiphenyl (TFMB) and 130micromole (mmol) of aminopropyl-terminated poly(dimethylsiloxane) areused to give the PI synthesis solution.

The above methods can be used to produce amino-terminated polyimidecompounds. However, other methods can be used to producecarboxy-terminated polyimide compounds. In addition, in the abovereaction between anhydride and diamine, where the backbone of theanhydride comprises a carbon-carbon triple bond, the affinity of thecarbon-carbon triple bond can promote the molecular structure.Alternatively, a diamine comprising vinyl siloxane structure can beused.

The molar ratio of dianhydride to diamine may be 1:1. The molarpercentage of the diamine comprising a functional group having activehydrogen may be 5˜25% of the total amount of diamine. The temperatureunder which the polyimide is synthesized is preferably 80˜250° C., morepreferably 100˜200° C. The reaction time may vary depending on the sizeof the batch. For example, the reaction time for obtaining 10˜30 gpolyimide is 6˜10 hours.

The organosilicon-modified polyimide can be classified as fluorinatedaromatic organosilicon-modified polyimides and aliphaticorganosilicon-modified polyimides. The fluorinated aromaticorganosilicon-modified polyimides are synthesized from siloxane-typediamine, aromatic diamine comprising fluoro (F) group (or referred to asfluorinated aromatic diamine) and aromatic dianhydride comprising fluoro(F) group (or referred to as fluorinated aromatic anhydride). Thealiphatic organosilicon-modified polyimides are synthesized fromdianhydride, siloxane-type diamine and at least one diamine notcomprising aromatic structure (e.g., benzene ring) (or referred to asaliphatic diamine), or from diamine (one of which is siloxane-typediamine) and at least one dianhydride not comprising aromatic structure(e.g., benzene ring) (or referred to as aliphatic anhydride). Thealiphatic organosilicon-modified polyimide includes semi-aliphaticorganosilicon-modified polyimide and fully aliphaticorganosilicon-modified polyimide. The fully aliphaticorganosilicon-modified polyimide is synthesized from at least onealiphatic dianhydride, siloxane-type diamine and at least one aliphaticdiamine. The raw materials for synthesizing the semi-aliphaticorganosilicon-modified polyimide include at least one aliphaticdianhydride or aliphatic diamine. The raw materials required forsynthesizing the organosilicon-modified polyimide and the siloxanecontent in the organosilicon-modified polyimide would have certaineffects on transparency, chromism, mechanical property, warpage extentand refractivity of the substrate.

The organosilicon-modified polyimide of the present disclosure has asiloxane content of 20˜75 wt %, preferably 30˜70 wt %, and a glasstransition temperature of below 150° C. The glass transition temperature(Tg) is determined on TMA-60 manufactured by Shimadzu Corporation afteradding a thermal curing agent to the organosilicon-modified polyimide.The determination conditions include: load: 5 gram; heating rate: 10°C./min; determination environment: nitrogen atmosphere; nitrogen flowrate: 20 ml/min; temperature range: −40 to 300° C. When the siloxanecontent is below 20%, the film prepared from the organosilicon-modifiedpolyimide resin composition may become very hard and brittle due to thefilling of the phosphor and thermal conductive fillers, and tend to warpafter drying and curing, and therefore has a low processability. Inaddition, its resistance to thermochromism becomes lower. On the otherhand, when the siloxane content is above 75%, the film prepared from theorganosilicon-modified polyimide resin composition becomes opaque, andhas reduced transparency and tensile strength. Here, the siloxanecontent is the weight ratio of siloxane-type diamine (having a structureshown in Formula (A)) to the organosilicon-modified polyimide, whereinthe weight of the organosilicon-modified polyimide is the total weightof the diamine and the dianhydride used for synthesizing theorganosilicon-modified polyimide subtracted by the weight of waterproduced during the synthesis.

Wherein R is methyl or phenyl, preferably methyl, n is 1˜5, preferably1,2,3 or 5.

The only requirements on the organic solvent used for synthesizing theorganosilicon-modified polyimide are to dissolve theorganosilicon-modified polyimide and to ensure the affinity(wettability) to the phosphor or the fillers to be added. However,excessive residue of the solvent in the product should be avoided.Normally, the number of moles of the solvent is equal to that of waterproduced by the reaction between diamine and anhydride. For example, 1mol diamine reacts with 1 mol anhydride to give 1 mol water; then theamount of solvent is 1 mol. In addition, the organic solvent used has aboiling point of above 80° C. and below 300° C., more preferably above120° C. and below 250° C., under standard atmospheric pressure. Sincedrying and curing under a lower temperature are needed after coating, ifthe temperature is lower than 120° C., good coating cannot be achieveddue to high drying speed during the coating process. If the boilingpoint of the organic solvent is higher than 250° C., the drying under alower temperature may be deferred. Specifically, the organic solvent maybe an ether-type organic solvent, an ester-type organic solvent, adimethyl ether-type organic solvent, a ketone-type organic solvent, analcohol-type organic solvent, an aromatic hydrocarbon solvent or othersolvents. The ether-type organic solvent includes ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, propylene glycolmonomethyl ether, propylene glycol monoethyl ether, ethylene glycoldimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutylether, diethylene glycol dimethyl ether, diethylene glycol diethylether, diethylene glycol methyl ethyl ether, dipropylene glycol dimethylether or diethylene glycol dibutyl ether, and diethylene glycol butylmethyl ether. The ester-type organic solvent includes acetates,including ethylene glycol monoethyl ether acetate, diethylene glycolmonobutyl ether acetate, propylene glycol monomethyl ether acetate,propyl acetate, propylene glycol diacetate, butyl acetate, isobutylacetate, 3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, benzylacetate and 2-(2-butoxyethoxy)ethyl acetate; and methyl lactate, ethyllactate, n-butyl acetate, methyl benzoate and ethyl benzoate. Thedimethyl ether-type solvent includes triethylene glycol dimethyl etherand tetraethylene glycol dimethyl ether. The ketone-type solventincludes acetylacetone, methyl propyl ketone, methyl butyl ketone,methyl isobutyl ketone, cyclopentanone, and 2-heptanone. Thealcohol-type solvent includes butanol, isobutanol, isopentanol,4-methyl-2-pentanol, 3-methyl-2-butanol, 3-methyl-3-methoxybutanol, anddiacetone alcohol. The aromatic hydrocarbon solvent includes toluene andxylene. Other solvents include γ-butyrolactone, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

The present disclosure provides an organosilicon-modified polyimideresin composition comprising the above organosilicon-modified polyimideand a thermal curing agent, which may be epoxy resin, hydrogenisocyanate or bisoxazoline compound. In one embodiment, based on theweight of the organosilicon-modified polyimide, the amount of thethermal curing agent is 5˜12% of the weight of theorganosilicon-modified polyimide. The organosilicon-modified polyimideresin composition may further comprise heat dispersing particles andphosphor.

Light Transmittance

The factors affecting the light transmittance of theorganosilicon-modified polyimide resin composition at least include thetype of the main material, the type of the modifier (thermal curingagent), the type and content of the heat dispersing particles, and thesiloxane content. Light transmittance refers to the transmittance of thelight near the main light-emitting wavelength range of the LED chip. Forexample, blue LED chip has a main light-emitting wavelength of around450 nm, then the composition or the polyimide should have low enough oreven no absorption to the light having a wavelength around 450 nm, so asto ensure that most or even all the light can pass through thecomposition or the polyimide. In addition, when the light emitted by theLED chip passes through the interface of two materials, the closer therefractive indexes of the two materials, the higher the light outputefficiency. In order to be close to the refractive index of the material(such as die bonding glue) contacting with the filament substrate (orbase layer), the organosilicon-modified polyimide composition has arefractive index of 1.4˜1.7, preferably 1.4˜1.55. In order to use theorganosilicon-modified polyimide resin composition as substrate in thefilament, the organosilicon-modified polyimide resin composition isrequired to have good light transmittance at the peak wavelength ofInGaN of the blue-excited white LED. In order to obtain a goodtransmittance, the raw materials for synthesizing theorganosilicon-modified polyimide, the thermal curing agent and the heatdispersing particles can be adjusted. Because the phosphor in theorganosilicon-modified polyimide resin composition may have certaineffect on the transmittance test, the organosilicon-modified polyimideresin composition used for the transmittance test does not comprisephosphor. Such an organosilicon-modified polyimide resin composition hasa transmittance of 86˜93%, preferably 88˜91%, or preferably 89˜92%, orpreferably 90˜93%.

In the reaction of anhydride and diamine to produce polyimide, theanhydride and the diamine may vary. In other words, the polyimidesproduced from different anhydrides and different diamines may havedifferent light transmittances. The aliphatic organosilicon-modifiedpolyimide resin composition comprises the aliphaticorganosilicon-modified polyimide and the thermal curing agent, while thefluorinated aromatic organosilicon-modified polyimide resin compositioncomprises the fluorinated aromatic organosilicon-modified polyimide andthe thermal curing agent. Since the aliphatic organosilicon-modifiedpolyimide has an alicyclic structure, the aliphaticorganosilicon-modified polyimide resin composition has a relatively highlight transmittance. In addition, the fluorinated aromatic,semi-aliphatic and full aliphatic polyimides all have good lighttransmittance in respect of the blue LED chips. The fluorinated aromaticorganosilicon-modified polyimide is synthesized from a siloxane-typediamine, an aromatic diamine comprising a fluoro (F) group (or referredto as fluorinated aromatic diamine) and an aromatic dianhydridecomprising a fluoro (F) group (or referred to as fluorinated aromaticanhydride). In other words, both Ar¹ and Ar² comprise a fluoro (F)group. The semi-aliphatic and full aliphatic organosilicon-modifiedpolyimides are synthesized from a dianhydride, a siloxane-type diamineand at least one diamine not comprising an aromatic structure (e.g. abenzene ring) (or referred to as aliphatic diamine), or from a diamine(one of the diamine is siloxane-type diamine) and at least onedianhydride not comprising an aromatic structure (e.g. a benzene ring)(or referred to as aliphatic anhydride). In other words, at least one ofAr¹ and Ar² has an alicyclic hydrocarbon structure.

Although blue LED chips have a main light-emitting wavelength of 450 nm,they may still emit a minor light having a shorter wavelength of around400 nm, due to the difference in the conditions during the manufactureof the chips and the effect of the environment. The fluorinatedaromatic, semi-aliphatic and full aliphatic polyimides have differentabsorptions to the light having a shorter wavelength of 400 nm. Thefluorinated aromatic polyimide has an absorbance of about 20% to thelight having a shorter wavelength of around 400 nm, i.e. the lighttransmittance of the light having a wavelength of 400 nm is about 80%after passing through the fluorinated aromatic polyimide. Thesemi-aliphatic and full aliphatic polyimides have even lower absorbanceto the light having a shorter wavelength of 400 nm than the fluorinatedaromatic polyimide, which is only 12%. Accordingly, in an embodiment, ifthe LED chips used in the LED filament have a uniform quality, and emitless blue light having a shorter wavelength, the fluorinated aromaticorganosilicon-modified polyimide may be used to produce the filamentsubstrate or the light-conversion layer. In another embodiment, if theLED chips used in the LED filament have different qualities, and emitmore blue light having a shorter wavelength, the semi-aliphatic or fullaliphatic organosilicon-modified polyim ides may be used to produce thefilament substrate or the light-conversion layer.

Adding different thermal curing agents imposes different effects on thelight transmittance of the organosilicon-modified polyimide. Table 1-1shows the effect of the addition of different thermal curing agents onthe light transmittance of the full aliphatic organosilicon-modifiedpolyimide. At the main light-emitting wavelength of 450 nm for the blueLED chip, the addition of different thermal curing agents renders nosignificant difference to the light transmittance of the full aliphaticorganosilicon-modified polyimide; while at a short wavelength of 380 nm,the addition of different thermal curing agents does affect the lighttransmittance of the full aliphatic organosilicon-modified polyimide.The organosilicon-modified polyimide itself has a poorer transmittanceto the light having a short wavelength (380 nm) than to the light havinga long wavelength (450 nm). However, the extent of the difference varieswith the addition of different thermal curing agents. For example, whenthe thermal curing agent KF105 is added to the full aliphaticorganosilicon-modified polyimide, the extent of the reduction in thelight transmittance is less. In comparison, when the thermal curingagent 2021 p is added to the full aliphatic organosilicon-modifiedpolyimide, the extent of the reduction in the light transmittance ismore. Accordingly, in an embodiment, if the LED chips used in the LEDfilament have a uniform quality, and emit less blue light having a shortwavelength, the thermal curing agent BPA or the thermal curing agent2021 p may be added. In comparison, in an embodiment, if the LED chipsused in the LED filament have different qualities, and emit more bluelight having a short wavelength, the thermal curing agent KF105 may beused. Both Table 1-1 and Table 1-2 show the results obtained in thetransmittance test using Shimadzu UV-Vis Spectrometer UV-1800. The lighttransmittances at wavelengths 380 nm, 410 nm and 450 nm are tested basedon the light emission of white LEDs.

TABLE 1-1 Organosilicon- Film Tensile Modified Amount 380 410 450Thickness Elongation Strength Polyimides Types (%) nm nm nm (μm) (%)(MPa) Full Aliphatic BPA 8.0 87.1 89.1 90.6 44 24.4 10.5 Full AliphaticX22-163 8.0 86.6 88.6 90.2 44 43.4 8.0 Full Aliphatic KF105 8.0 87.288.9 90.4 44 72.6 7.1 Full Aliphatic EHPE3150 8.0 87.1 88.9 90.5 44 40.913.1 Full Aliphatic 2021p 8.0 86.1 88.1 90.1 44 61.3 12.9

TABLE 1-2 Thermal Curing Light Transmittance (%) Mechanical StrengthOrganosilicon- Agent Film Tensile Modified Amount 380 410 450 ThicknessElongation Strength Polyimide Type (%) nm nm nm (mm) (%) (MPa) FullAliphatic BPA 4.0 86.2 88.4 89.7 44 22.5 9.8 Full Aliphatic 8.0 87.189.1 90.6 44 24.4 10.5 Full Aliphatic 12.0 87.3 88.9 90.5 44 20.1 9.0

Even when the same thermal curing agent is added, different added amountthereof will have different effects on the light transmittance. Table1-2 shows that when the added amount of the thermal curing agent BPA tothe full aliphatic organosilicon-modified polyimide is increased from 4%to 8%, the light transmittance increases. However, when the added amountis further increased to 12%, the light transmittance keeps almostconstant. It is shown that the light transmittance increases with theincrease of the added amount of the thermal curing agent, but after thelight transmittance increases to certain degree, adding more thermalcuring agent will have limited effect on the light transmittance.

Different heat dispersing particles would have different transmittances.If heat dispersing particles with low light transmittance or low lightreflection are used, the light transmittance of theorganosilicon-modified polyimide resin composition will be lower. Theheat dispersing particles in the organosilicon-modified polyimide resincomposition of the present disclosure are preferably selected to betransparent powders or particles with high light transmittance or highlight reflection. Since the soft filament for the LED is mainly for thelight emission, the filament substrate should have good lighttransmittance. In addition, when two or more types of heat dispersingparticles are mixed, particles with high light transmittance and thosewith low light transmittance can be used in combination, wherein theproportion of particles with high light transmittance is higher thanthat of particles with low light transmittance. In an embodiment, forexample, the weight ratio of particles with high light transmittance toparticles with low light transmittance is 3˜5:1.

Different siloxane content also affects the light transmittance. As canbe seen from Table 2, when the siloxane content is only 37 wt %, thelight transmittance is only 85%. When the siloxane content is increaseto above 45%, the light transmittance exceeds 94%.

TABLE 2 Organosilicon- Siloxane Thermal Tensile Elastic ElongationModified Content Curing Tg Strength Modulus at Break Chemical Resistanceto Polyimide (wt %) Agent (° C.) (MPa) (GPa) (%) TransmittanceResistance Thermochromism 1 37 BPA 158 33.2 1.7 10 85 Δ 83 2 41 BPA 14238.0 1.4 12 92 ∘ 90 3 45 BPA 145 24.2 1.1 15 97 Δ 90 4 64 BPA 30 8.90.04 232 94 ∘ 92 5 73 BPA 0 1.8 0.001 291 96 ∘ 95

Heat Resistance

The factors affecting the heat resistance of the organosilicon-modifiedpolyimide resin composition include at least the type of the mainmaterial, the siloxane content, and the type and content of the modifier(thermal curing agent).

All the organosilicon-modified polyimide resin composition synthesizedfrom fluorinated aromatic, semi-aliphatic and, full aliphaticorganosilicon-modified polyimide have superior heat resistance, and aresuitable for producing the filament substrate or the light-conversionlayer. Detailed results from the accelerated heat resistance and agingtests (300° C.×1 hr) show that the fluorinated aromaticorganosilicon-modified polyimide has better heat resistance than thealiphatic organosilicon-modified polyimide. Accordingly, in anembodiment, if a high power, high brightness LED chip is used as the LEDfilament, the fluorinated aromatic organosilicon-modified polyimide maybe used to produce the filament substrate or the light-conversion layer.

The siloxane content in the organosilicon-modified polyimide will affectthe resistance to thermochromism of the organosilicon-modified polyimideresin composition. The resistance to thermochromism refers to thetransmittance determined at 460 nm after placing the sample at 200° C.for 24 hours. As can be seen from Table 2, when the siloxane content isonly 37 wt %, the light transmittance after 24 hours at 200° C. is only83%. As the siloxane content is increased, the light transmittance after24 hours at 200° C. increases gradually. When the siloxane content is 73wt %, the light transmittance after 24 hours at 200° C. is still as highas 95%. Accordingly, increasing the siloxane content can effectivelyincrease the resistance to thermochromism of the organosilicon-modifiedpolyimide.

Adding a thermal curing agent can lead to increased heat resistance andglass transition temperature. As shown in FIGS. 4, A1 and A2 representthe curves before and after adding the thermal curing agent,respectively; and the curves D1 and D2 represent the values afterdifferential computation on curves A1 and A2, respectively, representingthe extent of the change of curves A1 and A2. As can be seen from theanalysis results from TMA (thermomechanical analysis) shown in FIG. 4,the addition of the thermal curing agent leads to a trend that thethermal deformation slows down. Accordingly, adding a thermal curingagent can lead to increase of the heat resistance.

In the cross-linking reaction between the organosilicon-modifiedpolyimide and the thermal curing agent, the thermal curing agent shouldhave an organic group which is capable of reacting with the functionalgroup having active hydrogen in the polyimide. The amount and the typeof the thermal curing agent have certain effects on chromism, mechanicalproperty and refractive index of the substrate. Accordingly, a thermalcuring agent with good heat resistance and transmittance can beselected. Examples of the thermal curing agent include epoxy resin,isocyanate, bismaleimide, and bisoxazoline compounds. The epoxy resinmay be bisphenol A epoxy resin, such as BPA; or siloxane-type epoxyresin, such as KF105, X22-163, and X22-163A; or alicylic epoxy resin,such as 3,4-epoxycyclohexylmethyl3,4-epoxycyclohexanecarboxylate(2021P), EHPE3150, and EHPE3150CE. Through the bridging reaction by theepoxy resin, a three dimensional bridge structure is formed between theorganosilicon-modified polyimide and the epoxy resin, increasing thestructural strength of the adhesive itself. In an embodiment, the amountof the thermal curing agent may be determined according to the molaramount of the thermal curing agent reacting with the functional grouphaving active hydrogen in the organosilicon-modified polyimide. In anembodiment, the molar amount of the functional group having activehydrogen reacting with the thermal curing agent is equal to that of thethermal curing agent. For example, when the molar amount of thefunctional group having active hydrogen reacting with the thermal curingagent is 1 mol, the molar amount of the thermal curing agent is 1 mol.

Thermal Conductivity

The factors affecting the thermal conductivity of theorganosilicon-modified polyimide resin composition include at least thetype and content of the phosphor, the type and content of the heatdispersing particles and the addition and the type of the couplingagent. In addition, the particle size and the particle size distributionof the heat dispersing particles would also affect the thermalconductivity.

The organosilicon-modified polyimide resin composition may also comprisephosphor for obtaining the desired light-emitting properties. Thephosphor can convert the wavelength of the light emitted from thelight-emitting semiconductor. For example, yellow phosphor can convertblue light to yellow light, and red phosphor can convert blue light tored light. Examples of yellow phosphor include transparent phosphor suchas (Ba,Sr,Ca)₂SiO₄:Eu, and (Sr,Ba)₂SiO₄:Eu (barium orthosilicate (BOS));silicate-type phosphor having a silicate structure such as Y₃Al₅O₁₂:Ce(YAG (yttrium⋅aluminum⋅garnet):Ce), and Tb₃Al₃O₁₂:Ce (YAG(terbium⋅aluminum⋅garnet):Ce); and oxynitride phosphor such asCa-α-SiAlON. Examples of red phosphor include nitride phosphor, such asCaAlSiN₃:Eu, and CaSiN₂:Eu. Examples of green phosphor include rareearth-halide phosphor, and silicate phosphor. The ratio of the phosphorin the organosilicon-modified polyimide resin composition may bedetermined arbitrarily according to the desired light-emitting property.In addition, since the phosphor have a thermal conductivity which issignificantly higher than that of the organosilicon-modified polyimideresin, the thermal conductivity of the organosilicon-modified polyimideresin composition as a whole will increase as the ratio of the phosphorin the organosilicon-modified polyimide resin composition increases.Accordingly, in an embodiment, as long as the light-emitting property isfulfilled, the content of the phosphor can be suitably increased toincrease the thermal conductivity of the organosilicon-modifiedpolyimide resin composition, which is beneficial to the heat dissipationof the filament substrate or the light-conversion layer. Furthermore,when the organosilicon-modified polyimide resin composition is used asthe filament substrate, the content, shape and particle size of thephosphor in the organosilicon-modified polyimide resin composition alsohave certain effect on the mechanical property (such as the elasticmodulus, elongation, tensile strength) and the warpage extent of thesubstrate. In order to render superior mechanical property and thermalconductivity as well as small warpage extent to the substrate, thephosphor included in the organosilicon-modified polyimide resincomposition are particulate, and the shape thereof may be sphere, plateor needle, preferably sphere. The maximum average length of the phosphor(the average particle size when they are spherical) is above 0.1 μm,preferably over 1 μm, further preferably 1˜100 μm, and more preferably1˜50 μm. The content of phosphor is no less than 0.05 times, preferablyno less than 0.1 times, and no more than 8 times, preferably no morethan 7 times, the weight of the organosilicon-modified polyimide. Forexample, when the weight of the organosilicon-modified polyimide is 100parts in weight, the content of the phosphor is no less than 5 parts inweight, preferably no less than 10 parts in weight, and no more than 800parts in weight, preferably no more than 700 parts in weight. When thecontent of the phosphor in the organosilicon-modified polyimide resincomposition exceeds 800 parts in weight, the mechanical property of theorganosilicon-modified polyimide resin composition may not achieve thestrength as required for a filament substrate, resulting in the increaseof the defective rate of the product. In an embodiment, two kinds ofphosphor are added at the same time. For example, when red phosphor andgreen phosphor are added at the same time, the added ratio of redphosphor to green phosphor is 1:5˜8, preferably 1:6˜7. In anotherembodiment, red phosphor and yellow phosphor are added at the same time,wherein the added ratio of red phosphor to yellow phosphor is 1:5˜8,preferably 1:6˜7. In another embodiment, three or more kinds of phosphorare added at the same time.

The main purposes of adding the heat dispersing particles are toincrease the thermal conductivity of the organosilicon-modifiedpolyimide resin composition, to maintain the color temperature of thelight emission of the LED chip, and to prolong the service life of theLED chip. Examples of the heat dispersing particles include silica,alumina, magnesia, magnesium carbonate, aluminum nitride, boron nitrideand diamond. Considering the dispersity, silica, alumina or combinationthereof is preferably. The shape of the heat dispersing particles may besphere, block, etc., where the sphere shape encompasses shapes which aresimilar to sphere. In an embodiment, heat dispersing particles may be ina shape of sphere or non-sphere, to ensure the dispersity of the heatdispersing particles and the thermal conductivity of the substrate,wherein the added weight ratio of the spherical and non-spherical heatdispersing particles is 1:0.15˜0.35.

Table 3-1 shows the relationship between the content of the heatdispersing particles and the thermal conductivity of theorganosilicon-modified polyimide resin composition. As the content ofthe heat dispersing particles increases, the thermal conductivity of theorganosilicon-modified polyimide resin composition increases. However,when the content of the heat dispersing particles in theorganosilicon-modified polyimide resin composition exceeds 1200 parts inweight, the mechanical property of the organosilicon-modified polyimideresin composition may not achieve the strength as required for afilament substrate, resulting in the increase of the defective rate ofthe product. In an embodiment, high content of heat dispersing particleswith high light transmittance or high reflectivity (such as SiO₂, Al₂O₃)may be added, which, in addition to maintaining the transmittance of theorganosilicon-modified polyimide resin composition, increases the heatdissipation of the organosilicon-modified polyimide resin composition.The heat conductivities shown in Tables 3-1 and 3-2 were measured by athermal conductivity meter DRL-III manufactured by Xiangtan cityinstruments Co., Ltd. under the following test conditions: heatingtemperature: 90° C.; cooling temperature: 20° C.; load: 350N, aftercutting the resultant organosilicon-modified polyimide resin compositioninto test pieces having a film thickness of 300 μm and a diameter of 30mm.

TABLE 3-1 Weight Ratio [wt %] 0.0% 37.9% 59.8% 69.8% 77.6% 83.9% 89.0%Volume Ratio [vol %] 0.0% 15.0% 30.0% 40.0% 50.0% 60.0% 70.0% ThermalConductivity[W/m*K] 0.17 0.20 0.38 0.54 0.61 0.74 0.81

TABLE 3-2 Specification 1 2 3 4 5 6 7 Average Particle Size[μm] 2.7 6.6  9.0  9.6  13 4.1  12 Particle Size 1~7 1~20 1~30 0.2~30 0.2~1100.1~20 0.1~100 Distribution[μm] Thermal 1.65 1.48 1.52 1.86 1.68 1.872.10 Conductivity[W/m*K]

For the effects of the particle size and the particle size distributionof the heat dispersing particles on the thermal conductivity of theorganosilicon-modified polyimide resin composition, see both Table 3-2and FIG. 5. Table 3-2 and FIG. 5 show seven heat dispersing particleswith different specifications added into the organosilicon-modifiedpolyimide resin composition in the same ratio and their effects on thethermal conductivity. The particle size of the heat dispersing particlessuitable to be added to the organosilicon-modified polyimide resincomposition can be roughly classified as small particle size (less than1 μm), medium particle size (1-30 μm) and large particle size (above 30μm).

Comparing specifications 1, 2 and 3, wherein only heat dispersingparticles with medium particle size but different average particle sizesare added, when only heat dispersing particles with medium particle sizeare added, the average particle size of the heat dispersing particlesdoes not significantly affect the thermal conductivity of theorganosilicon-modified polyimide resin composition. Comparingspecifications 3 and 4, wherein the average particle sizes are similar,the specification 4 comprising small particle size and medium particlesize obviously exhibits higher thermal conductivity than specification 3comprising only medium particle size. Comparing specifications 4 and 6,which comprise heat dispersing particles with both small particle sizeand medium particle size, although the average particle sizes of theheat dispersing particles are different, they have no significant effecton the thermal conductivity of the organosilicon-modified polyimideresin composition. Comparing specifications 4 and 7, specification 7,which comprises heat dispersing particles with large particle size inaddition to small particle size and medium particle size, exhibits themost excellent thermal conductivity. Comparing specifications 5 and 7,which both comprise heat dispersing particles with large, medium andsmall particle sizes and have similar average particle sizes, thethermal conductivity of specification 7 is significant superior to thatof specification 5 due to the difference in the particle sizedistribution. See FIG. 5 for the particle size distribution ofspecification 7, the curve is smooth, and the difference in the slope issmall, showing that specification 7 not only comprises each particlesize, but also have moderate proportions of each particle size, and theparticle size is normally distributed. For example, the small particlesize represents about 10%, the medium particle size represents about60%, and the large particle size represents about 30%. In contrast, thecurve for specification 5 has two regions with large slopes, whichlocate in the region of particle size 1-2 μm and particle size 30-70 μm,respectively, indicating that most of the particle size in specification5 is distributed in particle size 1-2 μm and particle size 30-70 μm, andonly small amount of heat dispersing particles with particle size 3-20μm are present, i.e. exhibiting a two-sided distribution.

Accordingly, the extent of the particle size distribution of the heatdispersing particles affecting the thermal conductivity is greater thanthat of the average particle size of the heat dispersing particles. Whenlarge, medium and small particle sizes of the heat dispersing particlesare added, and the small particle size represents about 5-20%, themedium particle size represents about 50-70%, and large particle sizerepresents about 20-40%, the organosilicon-modified polyimide resin willhave optimum thermal conductivity. That is because when large, mediumand small particle sizes are present, there would be denser packing andcontacting each other of heat dispersing particles in a same volume, soas to form an effective heat dissipating route.

In an embodiment, for example, alumina with a particle size distributionof 0.1˜100 μm and an average particle size of 12 μm or with a particlesize distribution of 0.1˜20 μm and an average particle size of 4.1 μm isused, wherein the particle size distribution is the range of theparticle size of alumina. In another embodiment, considering thesmoothness of the substrate, the average particle size may be selectedas ⅕˜⅖, preferably ⅕˜⅓ of the thickness of the substrate. The amount ofthe heat dispersing particles may be 1˜12 times the weight (amount) ofthe organosilicon-modified polyimide. For example, if the amount of theorganosilicon-modified polyimide is 100 parts in weight, the amount ofthe heat dispersing particles may be 100˜1200 parts in weight,preferably 400˜900 parts in weight. Two different heat dispersingparticles such as silica and alumina may be added at the same time,wherein the weight ratio of alumina to silica may be 0.4˜25:1,preferably 1˜10:1.

In the synthesis of the organosilicon-modified polyimide resincomposition, a coupling agent such as a silicone coupling agent may beadded to improve the adhesion between the solid material (such as thephosphor and/or the heat dispersing particles) and the adhesive material(such as the organosilicon-modified polyimide), and to improve thedispersion uniformity of the whole solid materials, and to furtherimprove the heat dissipation and the mechanical strength of thelight-conversion layer. The coupling agent may also be titanate couplingagent, preferably epoxy titanate coupling agent. The amount of thecoupling agent is related to the amount of the heat dispersing particlesand the specific surface area thereof. The amount of the couplingagent=(the amount of the heat dispersing particles*the specific surfacearea of the heat dispersing particles)/the minimum coating area of thecoupling agent. For example, when an epoxy titanate coupling agent isused, the amount of the coupling agent=(the amount of the heatdispersing particles*the specific surface area of the heat dispersingparticles)/331.5.

In other specific embodiments of the present invention, in order tofurther improve the properties of the organosilicon-modified polyimideresin composition in the synthesis process, an additive such as adefoaming agent, a leveling agent or an adhesive may be selectivelyadded in the process of synthesizing the organosilicon-modifiedpolyimide resin composition, as long as it does not affect lightresistance, mechanical strength, heat resistance and chromism of theproduct. The defoaming agent is used to eliminate the foams produced inprinting, coating and curing. For example, acrylic acid or siliconesurfactants may be used as the defoaming agent. The leveling agent isused to eliminate the bumps in the film surface produced in printing andcoating. Specifically, adding preferably 0.01˜2 wt % of a surfactantcomponent can inhibit foams. The coating film can be smoothened by usingacrylic acid or silicone leveling agents, preferably non-ionicsurfactants free of ionic impurities. Examples of the adhesive includeimidazole compounds, thiazole compounds, triazole compounds,organoaluminum compounds, organotitanium compounds and silane couplingagents. Preferably, the amount of these additives is no more than 10% ofthe weight of the organosilicon-modified polyimide. When the mixedamount of the additive exceeds 10 wt %, the physical properties of theresultant coating film tend to decline, and it even leads todeterioration of the light resistance due to the presence of thevolatile components.

Mechanical Strength

The factors affecting the mechanical strength of theorganosilicon-modified polyimide resin composition include at least thetype of the main material, the siloxane content, the type of themodifier (thermal curing agent), the phosphor and the content of theheat dispersing particles.

Different organosilicon-modified polyimide resins have differentproperties. Table 4 lists the main properties of the fluorinatedaromatic, semi-aliphatic and full aliphatic organosilicon-modifiedpolyimide, respectively, with a siloxane content of about 45% (wt %).The fluorinated aromatic has the best resistance to thermo chromism. Thefull aliphatic has the best light transmittance. The fluorinatedaromatic has both high tensile strength and high elastic modulus. Theconditions for testing the mechanical strengths shown in Table 4˜6: theorganosilicon-modified polyimide resin composition has a thickness of 50μm and a width of 10 mm, and the tensile strength of the film isdetermined according to ISO527-3:1995 standard with a drawing speed of10 mm/min.

TABLE 4 Organosilicon- Siloxane Thermal Tensile Elastic ElongationModified Content Curing Strength Modulus at Break Resistance toPolyimide (wt %) Agent (MPa) (GPa) (%) Transmittance ThermochromismFluorinated 44 X22-163 22.4 1.0 83 96 95 Aromatic Semi-Aliphatic 44X22-163 20.4 0.9 30 96 91 Full Aliphatic 47 X22-163 19.8 0.8 14 98 88

TABLE 5 Siloxane Addition of Thermal Tensile Elastic Elongation ContentPhosphor, Curing Tg Strength Modulus at Break Chemical Resistance to (wt%) Alumina Agent (° C.) (MPa) (GPa) (%) Transmittance ResistanceThermochromism 37 x BPA 158 33.2 1.7 10 85 Δ 83 37 ∘ BPA — 26.3 5.1 0.7— — — 41 x BPA 142 38.0 1.4 12 92 ∘ 90 41 ∘ BPA — 19.8 4.8 0.8 — — — 45x BPA 145 24.2 1.1 15 97 Δ 90 45 ∘ BPA — 21.5 4.2 0.9 — — — 64 x BPA  308.9 0.04 232 94 ∘ 92 64 ∘ BPA — 12.3 3.1 1.6 — — — 73 x BPA  0 1.8 0.001291 96 ∘ 95 73 ∘ BPA — 9.6 2.5 2 — — —

TABLE 6 Thermal Curing Transmittance (%) Mechanical StrengthOrganosilicon- Agent Film Tensile Modified Amount 380 410 450 ThicknessElongation Strength Polyimide Type (%) nm nm nm (μm) (%) (MPa) FullAliphatic BPA 8.0 87.1 89.1 90.6 44 24.4 10.5 Full Aliphatic X22-163 8.086.6 88.6 90.2 40 43.4 8.0 Full Aliphatic KF105 12.0 87.5 89.2 90.8 4380.8 7.5 Full Aliphatic EHPE3150 7.5 87.1 88.9 90.5 44 40.9 13.1 FullAliphatic 2021p 5.5 86.1 88.1 90.1 44 64.0 12.5

In the manufacture of the filament, the LED chip and the electrodes arefirst fixed on the filament substrate formed by theorganosilicon-modified polyimide resin composition with a die bondingglue, followed by a wiring procedure, in which electric connections areestablished between adjacent LED chips and between the LED chip and theelectrode with wires. To ensure the quality of die bonding and wiring,and to improve the product quality, the filament substrate should have acertain level of elastic modulus to resist the pressing force in the diebonding and wiring processes. Accordingly, the filament substrate shouldhave an elastic modulus more than 2.0 GPa, preferably 2˜6 GPa, morepreferably 4˜6 GPa. Table 5 shows the effects of different siloxanecontents and the presence of particles (phosphor and alumina) on theelastic modulus of the organosilicon-modified polyimide resincomposition. Where no fluorescent powder or alumina particle is added,the elastic modulus of the organosilicon-modified polyimide resincomposition is always less than 2.0 GPa, and as the siloxane contentincreases, the elastic modulus tends to decline, i.e. theorganosilicon-modified polyimide resin composition tends to soften.However, where phosphor and alumina particles are added, the elasticmodulus of the organosilicon-modified polyimide resin composition may besignificantly increased, and is always higher than 2.0 GPa. Accordingly,the increase in the siloxane content may lead to softening of theorganosilicon-modified polyimide resin composition, which isadvantageous for adding more fillers, such as more phosphor or heatdispersing particles. In order for the substrate to have superiorelastic modulus and thermal conductivity, appropriate particle sizedistribution and mixing ratio may be selected so that the averageparticle size is within the range from 0.1 μm to 100 μm or from 1 μm to50 μm.

In order for the LED filament to have good bending properties, thefilament substrate should have an elongation at break of more than 0.5%,preferably 1˜5%, most preferably 1.5˜5%. As shown in Table 5, where nofluorescent powder or alumina particle is added, theorganosilicon-modified polyimide resin composition has excellentelongation at break, and as the siloxane content increases, theelongation at break increases and the elastic modulus decreases, therebyreducing the occurrence of warpage. In contrast, where phosphor andalumina particles are added, the organosilicon-modified polyimide resincomposition exhibits decreased elongation at break and increased elasticmodulus, thereby increasing the occurrence of warpage.

By adding a thermal curing agent, not only the heat resistance and theglass transition temperature of the organosilicon-modified polyimideresin are increased, the mechanical properties, such as tensilestrength, elastic modulus and elongation at break, of theorganosilicon-modified polyimide are also increased. Adding differentthermal curing agents may lead to different levels of improvement. Table6 shows the tensile strength and the elongation at break of theorganosilicon-modified polyimide resin composition after the addition ofdifferent thermal curing agents. For the full aliphaticorganosilicon-modified polyimide, the addition of the thermal curingagent EHPE3150 leads to good tensile strength, while the addition of thethermal curing agent KF105 leads to good elongation.

TABLE 7 Specific Information of BPA Content of Viscosity HydrolysableEquivalent Product at 25° C. Color Chlorine of Epoxy Hue Name (mPa · s)(G) (mg/kg) (g/mol) APHA BPA 11000~15000 ≤1 ≤300 184~194 ≤30

TABLE 8 Specific Information of 2021P Viscosity Specific Melting BoilingWater Equivalent Product at25° C. Gravity Point Point Content of EpoxyHue Name (mPa · s) (25/25° C.) (° C.) (° C./4 hPa) (%) (g/mol) APHA2021P 250 1.17 −20 188 0.01 130 10

TABLE 9 Specific Information of EHPE3150 and EHPE3150CE Equiva-Viscosity lent of at 25° C. Appear- Softening Epoxy Hue Product Name(mPa · s) ance Point (g/mol) APHA EHPE3150 — Trans- 75 177 20 (in parent25% Plate acetone Solid solution) EHPE3150CE 50,000 Light — 151 60Yellow Trans- parent Liquid

TABLE 10 Specific Information of PAME, KF8010, X22-161A, X22-161B,NH15D, X22-163, X22-163A and KF-105 Specific Refractive ProductViscosity at Gravity Index at Equivalent of Name 25° C.(mm2/s) at 25° C.25° C. Functional Group PAME 4 0.90 1.448 130 g/mol KF8010 12 1.00 1.418430 g/mol X22-161A 25 0.97 1.411 800 g/mol X22-161B 55 0.97 1.408 1500g/mol NH15D 13 0.95 1.403 1.6~2.1 g/mmol X22-163 15 1.00 1.450 200 g/molX22-163A 30 0.98 1.413 1000 g/mol KF-105 15 0.99 1.422 490 g/mol

The organosilicon-modified polyimide resin composition of the presentembodiment may be used in a form of film or as a substrate together witha support to which it adheres. The film forming process comprises threesteps: (a) coating step: spreading the above organosilicon-modifiedpolyimide resin composition on a peelable body by coating to form afilm; (b) heating and drying step: heating and drying the film togetherwith the peelable body to remove the solvent from the film; and (c)peeling step: peeling the film from the peelable body after the dryingis completed to give the organosilicon-modified polyimide resincomposition in a form of film. The above peelable body may be acentrifugal film or other materials which do not undergo chemicalreaction with the organosilicon-modified polyimide resin composition,e.g., PET centrifugal film.

The organosilicon-modified polyimide resin composition may be adhered toa support to give an assembly film, which may be used as the substrate.The process of forming the assembly film comprises two steps: (a)coating step: spreading the above organosilicon-modified polyimide resincomposition on a support by coating to from an assembly film; and (b)heating and drying step: heating and drying the assembly film to removethe solvent from the film.

In the coating step, roll-to-roll coating devices such as roller coater,mold coating machine and blade coating machine, or simple coating meanssuch as printing, inkjeting, dispensing and spraying may be used.

The drying method in the above heating and drying step may be drying invacuum, drying by heating, or the like. The heating may be achieved by aheat source such as an electric heater or a heating media to produceheat energy and indirect convection, or by infrared heat radiationemitted from a heat source.

A film (composite film) with high thermal conductivity can be obtainedfrom the above organosilicon-modified polyimide resin composition bycoating and then drying and curing, so as to achieve any one orcombination of the following properties: superior light transmittance,chemical resistance, heat resistance, thermal conductivity, filmmechanical property and light resistance. The temperature and time inthe drying and curing step may be suitably selected according to thesolvent and the coated film thickness of the organosilicon-modifiedpolyimide resin composition. The weight change of theorganosilicon-modified polyimide resin composition before and after thedrying and curing as well as the change in the peaks in the IR spectrumrepresenting the functional groups in the thermal curing agent can beused to determine whether the drying and curing are completed. Forexample, when an epoxy resin is used as the thermal curing agent,whether the difference in the weight of the organosilicon-modifiedpolyimide resin composition before and after the drying and curing isequal to the weight of the added solvent as well as the increase ordecrease of the epoxy peak before and after the drying and curing areused to determine whether the drying and curing are completed.

In an embodiment, the amidation is carried out in a nitrogen atmosphere,or vacuum defoaming is employed in the synthesis of theorganosilicon-modified polyimide resin composition, or both, so that thevolume percentage of the cells in the organosilicon-modified polyimideresin composition composite film is 5˜20%, preferably 5˜10%. As shown inFIG. 6B, the organosilicon-modified polyimide resin compositioncomposite film is used as the substrate for the LED soft filament. Thesubstrate 420 b has an upper surface 420 b 1 and an opposite lowersurface 420 b 2. FIG. 6A shows the surface morphology of the substrateafter gold is scattered on the surface thereof as observed with vega3electron microscope from Tescan Corporation. As can be seen from FIG. 6Band the SEM image of the substrate surface shown in FIG. 6A, there is acell 4 d in the substrate, wherein the cell 4 d represents 5˜20% byvolume, preferably 5˜10% by volume, of the substrate 420 b, and thecross section of the cell 4 d is irregular. FIG. 6B shows thecross-sectional scheme of the substrate 420 b, wherein the dotted lineis the baseline. The upper surface 420 b 1 of the substrate comprises afirst area 4 a and a second area 4 b, wherein the second area 4 bcomprises a cell 4 d, and the first area 4 a has a surface roughnesswhich is less than that of the second area 4 b. The light emitted by theLED chip passes through the cell in the second area and is scattered, sothat the light emission is more uniform. The lower surface 420 b 2 ofthe substrate comprises a third area 4 c, which has a surface roughnesswhich is higher than that of the first area 4 a. When the LED chip ispositioned in the first area 4 a, the smoothness of the first area 4 ais favorable for subsequent bonding and wiring. When the LED chip ispositioned in the second area 4 b or the third area 4 c, the area ofcontact between the die bonding glue and substrate is large, whichimproves the bonding strength between the die bonding glue andsubstrate. Therefore, by positioning the LED chip on the upper surface420 b 1, bonding and wiring as well as the bonding strength between thedie bonding glue and substrate can be ensured at the same time. When theorganosilicon-modified polyimide resin composition is used as thesubstrate of the LED soft filament, the light emitted by the LED chip isscattered by the cell in the substrate, so that the light emission ismore uniform, and glare can be further improved at the same time. In anembodiment, the surface of the substrate 420 b may be treated with asilicone resin or a titanate coupling agent, preferably a silicone resincomprising methanol or a titanate coupling agent comprising methanol, ora silicone resin comprising isopropanol. The cross section of thetreated substrate is shown in FIG. 6C. The upper surface 420 b 1 of thesubstrate has relatively uniform surface roughness. The lower surface420 b 2 of the substrate comprises a third area 4 c and a fourth area 4e, wherein the third area 4 c has a surface roughness which is higherthan that of the fourth area 4 e. The surface roughness of the uppersurface 420 b 1 of the substrate may be equal to that of the fourth area4 e. The surface of the substrate 420 b may be treated so that amaterial with a high reactivity and a high strength can partially enterthe cell 4 d, so as to improve the strength of the substrate.

When the organosilicon-modified polyimide resin composition is preparedby vacuum defoaming, the vacuum used in the vacuum defoaming may be−0.5˜−0.09 MPa, preferably −0.2˜−0.09 MPa. When the total weight of theraw materials used in the preparation of the organosilicon-modifiedpolyimide resin composition is less than or equal to 250 g, therevolution speed is 1200˜2000 rpm, the rotation speed is 1200˜2000 rpm,and time for vacuum defoaming is 3˜8 min. This not only maintainscertain amount of cells in the film to improve the uniformity of lightemission, but also keeps good mechanical properties. The vacuum may besuitably adjusted according to the total weight of the raw materialsused in the preparation of the organosilicon-modified polyimide resincomposition. Normally, when the total weight is higher, the vacuum maybe reduced, while the stirring time and the stirring speed may besuitably increased.

According to the present disclosure, a resin having superiortransmittance, chemical resistance, resistance to thermochromism,thermal conductivity, film mechanical property and light resistance asrequired for a LED soft filament substrate can be obtained. In addition,a resin film having a high thermal conductivity can be formed by simplecoating methods such as printing, inkjeting, and dispensing.

When the organosilicon-modified polyimide resin composition compositefilm is used as the filament substrate (or base layer), the LED chip isa hexahedral luminous body. In the production of the LED filament, atleast two sides of the LED chip are coated by a top layer. When theprior art LED filament is lit up, non-uniform color temperatures in thetop layer and the base layer would occur, or the base layer would give agranular sense. Accordingly, as a filament substrate, the composite filmis required to have superior transparency. In other embodiments,sulfonyl group, non-coplanar structure, meta-substituted diamine, or thelike may be introduced into the backbone of the organosilicon-modifiedpolyimide to improve the transparency of the organosilicon-modifiedpolyimide resin composition. In addition, in order for the bulbemploying said filament to achieve omnidirectional illumination, thecomposite film as the substrate should have certain flexibility.Therefore, flexible structures such as ether (such as(4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenyl ether), carbonyl,methylene may be introduced into the backbone of theorganosilicon-modified polyimide. In other embodiments, a diamine ordianhydride comprising a pyridine ring may be employed, in which therigid structure of the pyridine ring can improve the mechanicalproperties of the composite film. Meanwhile, by using it together with astrong polar group such as —F, the composite film may have superiorlight transmittance. Examples of the anhydride comprising a pyridinering include2,6-bis(3′,4′-dicarboxyphenyl)-4-(3″,5″-bistrifluoromethylphenyl)pyridinedianhydride.

The LED filament structure in the aforementioned embodiments is mainlyapplicable to the LED light bulb product, so that the LED light bulb canachieve the omni-directional light illuminating effect through theflexible bending characteristics of the single LED filament. Thespecific embodiment in which the aforementioned LED filament applied tothe LED light bulb is further explained below.

Please refer to FIG. 7A. FIG. 7A illustrates a perspective view of anLED light bulb according to the third embodiment of the presentdisclosure. According to the third embodiment, the LED light bulb 20 ccomprises a lamp housing 12, a bulb base 16 connected with the lamphousing 12, two conductive supports 51 a, 51 b disposed in the lamphousing 12, a driving circuit 518 electrically connected with both theconductive supports 51 a, 51 b and the bulb base 16, a stem 19,supporting arms 15 and a single LED filament 100.

The lamp housing 12 is a material which is preferably light transmissiveor thermally conductive, such as, glass or plastic, but not limitedthereto. In implementation, the lamp housing 12 may be doped with agolden yellow material or its surface coated with a yellow film toabsorb a portion of the blue light emitted by the LED chip to reduce thecolor temperature of the light emitted by the LED light bulb 20 c. Inother embodiments of the present invention, the lamp housing 12 includesa layer of luminescent material (not shown), which may be formed on theinner surface or the outer surface of the lamp housing 12 according todesign requirements or process feasibility, or even integrated in thematerial of the lamp housing 12. The luminescent material layercomprises low reabsorption semiconductor nanocrystals (hereinafterreferred to as quantum dots), the quantum dots comprises a core, aprotective shell and a light absorbing shell, and the light absorbingshell is disposed between the core and the protective shell. The coreemits the emissive light with emission wavelength, and the lightabsorbing shell emits the excited light with excitation wavelength. Theemission wavelength is longer than the excitation wavelength, and theprotective shell provides the stability of the light.

The core is a semiconductor nanocrystalline material, typically thecombination of at least of one metal and at least one non-metal. Thecore is prepared by combining a coation precursor(s) with an anionprecursor(s). The metal for the core is most preferably selected fromZn, Cd, Hg, Ga, In, Ti, Pb or a rare earth. The non-metal is mostpreferably selected from O, S, Se, P, As or Te. The cationic precursorion may include all transition metals and rare earth elements, and theanionic precursor ions may be choosen from O, S, Se, Te, N, P, As, F,CL, and Br. Furthermore, cationic precursors may include elements orcompounds, such as elements, covalent compounds, or ionic compounds,including but are not limited to, oxides, hydroxides, coordinationcompounds, or metal salts, which serves as a source for theelectropositive element or elements in the resulting nanocrystal core orshell materials.

The cationic precursor solution may include a metal oxide, a metalhalide, a metal nitride, a metal ammonia complex, a metal amine, a metalamide, a metal imide, a metal carboxylate, a metal acetylacetonate, ametal dithiolate, a metal carbonyl, a metal cyanide, a metal isocyanide,a metal nitrile, a metal peroxide, a metal hydroxide, a metal hydride, ametal ether complex, a metal diether complex, a metal triether compound,a metal carbonate, a metal nitrate, a metal nitrite, a metal sulfate, ametal alkoxide, a metal siloxide, a metal thiolate, a metal dithiolate,a metal disulfide, a metal carbamate, a metal dialky carbamate, a metalpyridine complex, a metal dipyridine complex, a metal phenanthrolinecomplex, a metal terpyridine complex, a metal diamine complex, a metaltriamine complex, a metal diimine, a metal pyridine diimine, a metalpyrazollborate, a metal bis(pyrazole)borate, a metaltris(pyrazole)borate, a metal nitrosyl, a metal thiocarbamate, metaldiazabutadiene, a metal dithiocarbamate, a metal dialkylacetamide, ametal dialkylformamide, a metal formamidinate, a metal phosphinecomplex, a metal arsine complex, a metal diphosphine complex, a metaldiarsine complex, a metal oxalate, a metal imidazole, a metalpyrazolate, a metal Schiff base complex, a metal porphyrin, a metalphthalocyanine, a metal subphthalocyanine, a metal picolinate, a metalpiperidine complex, a metal pyrazolyl, a metal salicylaldehyde, a metalethylenediamine, a metal triflate compound or any combination thereof.Preferably, the cationic precursor solution may include a metal oxide, ametal carbonate, a metal bicarbonate, a metal sulfate, a metal sulfite,a metal phosphate, a metal phosphite, a metal halide, a metalcarboxylate, a metal hydroxide, a metal alkoxide, a metal thiolate, ametal amide, a metal imide, a metal alkyl, a metal aryl, a metalcoordination complex, a metal solvate, a metal salt or a combinationthereof. Most preferably, the cationic precursor is a metal oxide ormetal salt precursor and may be selected from zinc stearate, zincmyristate, zinc acetate, and manganese stearate.

Anionic precursors may also include elements, covalent compounds, orionic compounds, which are used as one or more electronegative elementsin the resulting nanocrystals. These definitions expect to be able toprepare ternary compounds, quaternary compounds and even more complexspecies using the methods disclosed in the present invention, in whichcase more than one cationic precursor and/or more than one anionprecursor can be used. When two or more cationic elements are usedduring a given monolayer growth, if the other part of thenanocrystalline contains only a single cationic, the resultingnanocrystals have a cationic alloy at the specified single layer. Thesame method can be used to prepare nanocrystals with anionic alloys.

The above method is applicable to the core/shell nanocrystals preparedusing a series of cationic precursor compounds of core and shellmaterials, for example, precursors of Group II metals (eg, Zn, Cd orHg), precursors of Group III metals (eg, Al, Ga or In), a precursor of aGroup IV metal (for example, Ge, Sn or Pb), or a transition metal (forexample, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc), Re, Fe, Ru, Os, Co,Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, etc.).

The components of the light absorbing shell may be the same or differentfrom the composition of the core. Typically, the light absorbing shellmaterial has the same lattice structure as the material selected for thecore. For example, if CdSe is used as the emission region material, theabsorption region material may be CdS. The light absorbing shellmaterial is chosen to provide good absorption characteristics and candepend on the light source. For example, CdS can be a good choice forthe absorption region when the excitation comes from a typical blue LED(within the wavelength range between 440 and 470 nm) solid stateillumination. For example, if the excitation originates from a purpleLED to produce a red LED by frequency down-conversion, then ZnSe orZnSe_(x)S_(1-x) (where x is greater than or equal to 0 and less than orequal to 1) is a preferred choice for the absorption region. As anotherexample, if one wishes to obtain near-infrared emission from a quantumdot for bio-medical applications (700-1000 nm) by using a red lightsource, then CdSe and InP often work as the absorption region material.

The protected area (wide bandgap semiconductor or insulator) at theoutermost outer shell of the quantum dot provides the desired chemicaland optical stability to the quantum dots. In general, a protectiveshell (also known as a protected area) neither effectively absorbs lightnor emits directional photons within the preferred excitation windowdescribed above. This is because it has a wide band gap. For example,ZnS and GaN are examples of protective shell materials. Metal oxides canalso be utilized. In certain embodiments, an organic polymer can be usedas a protective shell. The thickness of the protective shell istypically in the range between 1 and 20 monolayers. Moreover, thethickness can also be increased as needed, but this also increasesproduction costs.

A light absorbing shell includes a plurality of mono layers that form acompositional gradient. For example, the light absorbing shell caninclude three components varying in a ratio of 1:0:1 in a mono layerlocated closest to the core to a ratio 0:1:1 in a mono layer locatedclosest to the protective shell. By way of example, three usefulcomponents are Cd, Zn, and S and for instance, a mono layer closest tothe core may have a component CdS (ratio 1:0:1), a mono layer closest tothe protective shell may have a component corresponding to ZnS (Ratio0:1:1), and the intermediate mono layer between the core and theprotective shell may have a component corresponding to ZnSe_(x)S_(1-x)having a ratio (X): (1−X): 1, and wherein X greater than or equal to 0and less than or equal to 1. In this case, X is larger for a mono layercloser to the core than a mono layer that closer to the protectiveshell. In another embodiment, the transition shell consists of threecomponents, the ratio from the single layer closest to the core to thesingle layer closest to the protective shell: 0.9:0.1:1, 0.8:0.2:1,0.6:0.4:1, 0.4:0.6:1, and 0.2:0.8:1. Other combinations of Cd, Zn, S,and Se alloys can also be used as transition shells instead ofZnSe_(x)S_(1-x) as long as they have suitable lattice matchingparameters. In one embodiment, a suitable transition shell includes oneshell having Cd, Zn, and S components and the following layers listedfrom the layer closest to the light absorbing shell to the layer closestto the protective shell: Cd_(0.9)Zn_(0.1)S, Cd_(0.8)Zn_(0.2)S,Cd_(0.6)Zn_(0.4)S, Cd_(0.4)Zn_(0.6)S, Cd_(0.2)Zn_(0.8)S.

The LED filament 100 shown in FIG. 7A is bent to form a contourresembling to a circle while being observed from the top view of FIG.7A. According to the embodiment of FIG. 7A, the LED filament 100 is bentto form a wave shape from side view. The shape of the LED filament 100is novel and makes the illumination more uniform. In comparison with aLED bulb having multiple LED filaments, single LED filament 100 has lessconnecting spots. In implementation, single LED filament 100 has onlytwo connecting spots such that the probability of defect soldering ordefect mechanical pressing is decreased.

The stem 19 has a stand 19 a extending to the center of the bulb shell12. The stand 19 a supports the supporting arms 15. The first end ofeach of the supporting arms 15 is connected with the stand 19 a whilethe second end of each of the supporting arms 15 is connected with theLED filament 100.

Please refer to FIG. 7B which illustrates an enlarged cross-sectionalview of the dashed-line circle of FIG. 7A. The second end of each of thesupporting arms 15 has a clamping portion 15 a which clamps the body ofthe LED filament 100. The clamping portion 15 a may, but not limited to,clamp at either the wave crest or the wave trough. Alternatively, theclamping portion 15 a may clamp at the portion between the wave crestand the wave trough. The shape of the clamping portion 15 a may betightly fitted with the outer shape of the cross-section of the LEDfilament 100. The dimension of the inner shape (through hole) of theclamping portion 15 a may be a little bit smaller than the outer shapeof the cross-section of the LED filament 100. During manufacturingprocess, the LED filament 100 may be passed through the inner shape ofthe clamping portion 15 a to form a tight fit. Alternatively, theclamping portion 15 a may be formed by a bending process. Specifically,the LED filament 100 may be placed on the second end of the supportingarm 15 and a clamping tooling is used to bend the second end into theclamping portion to clamp the LED filament 100.

The supporting arms 15 may be, but not limited to, made of carbon steelspring to provide with adequate rigidity and flexibility so that theshock to the LED light bulb caused by external vibrations is absorbedand the LED filament 100 is not easily to be deformed. Since the stand19 a extending to the center of the bulb shell 12 and the supportingarms 15 are connected to a portion of the stand 19 a near the topthereof, the position of the LED filaments 100 is at the level close tothe center of the bulb shell 12. Accordingly, the illuminationcharacteristics of the LED light bulb 20 c are close to that of thetraditional light bulb including illumination brightness. Theillumination uniformity of LED light bulb 20 c is better. In theembodiment, at least a half of the LED filaments 100 is around a centeraxle of the LED light bulb 20 c. The center axle is coaxial with theaxle of the stand 19 a.

In the embodiment, the first end of the supporting arm 15 is connectedwith the stand 19 a of the stem 19. The clamping portion of the secondend of the supporting arm 15 is connected with the outer insulationsurface of the LED filaments 100 such that the supporting arms 15 arenot used as connections for electrical power transmission. In anembodiment where the stem 19 is made of glass, the stem 19 would not becracked or exploded because of the thermal expansion of the supportingarms 15 of the LED light bulb 20 c. Additionally, there may be no standin an LED light bulb. The supporting arm 15 may be fixed to the stem orthe bulb shell directly to eliminate the negative effect to illuminationcaused by the stand.

The supporting arm 15 is thus non-conductive to avoid a risk that theglass stem 19 may crack due to the thermal expansion and contraction ofthe metal filament in the supporting arm 15 under the circumstances thatthe supporting arm 15 is conductive and generates heat when currentpasses through the supporting arm 15.

In different embodiments, the second end of the supporting arm 15 may bedirectly inserted inside the LED filament 100 and become an auxiliarypiece in the LED filament 100, which can enhance the mechanical strengthof the LED filament 100. Relative embodiments are described later.

The inner shape (the hole shape) of the clamping portion 15 a fits theouter shape of the cross section of the LED filament 100; therefore,based upon a proper design, the cross section of the LED filament 100may be oriented to face towards a predetermined orientation. Forexample, as shown in FIG. 7B, the LED filament 100 comprises a top layer420 a, LED chips 104, and a base layer 420 b. The LED chips 104 arealigned in line along the axial direction (or an elongated direction) ofthe LED filament 100 and are disposed between the top layer 420 a andthe base layer 420 b. The top layer 420 a of the LED filament 100 isoriented to face towards ten o'clock in FIG. 7B. A lighting face of thewhole LED filament 100 may be oriented to face towards the sameorientation substantially to ensure that the lighting face of the LEDfilament 100 is visually identical. The LED filament 100 comprises amain lighting face Lm and a subordinate lighting face Ls correspondingto the LED chips. If the LED chips in the LED filament 100 are wirebonded and are aligned in line, a face of the top layer 420 a away fromthe base layer 420 b is the main lighting face Lm, and a face of thebase layer 420 b away from the top layer 420 a is the subordinatelighting face Ls. The main lighting face Lm and the subordinate lightingface Ls are opposite to each other. When the LED filament 100 emitslight, the main lighting face Lm is the face through which the largestamount of light rays passes, and the subordinate lighting face Ls is theface through which the second largest amount of light rays passes. Inthe embodiment, there is, but is not limited to, a conductive foil 530formed between the top layer 420 a and the base layer 420 b, which isutilized for electrical connection between the LED chips. In theembodiment, the LED filament 100 wriggles with twists and turns whilethe main lighting face Lm is always towards outside. That is to say, anyportion of the main lighting face Lm is towards the bulb shell 12 or thebulb base 16 and is away from the stem 19 at any angle, and thesubordinate lighting face Ls is always towards the stem 19 or towardsthe top of the stem 19 (the subordinate lighting face Ls is alwaystowards inside).

The LED filament 100 shown in FIG. 7A is curved to form a circular shapein a top view while the LED filament is curved to form a wave shape in aside view. The wave shaped structure is not only novel in appearance butalso guarantees that the LED filament 100 illuminates evenly. In themeantime, the single LED filament 100, comparing to multiple LEDfilaments, requires less joint points (e.g., pressing points, fusingpoints, or welding points) for being connected to the conductivesupports 51 a, 51 b. In practice, the single LED filament 100 (as shownin FIG. 7A) requires only two joint points respectively formed on thetwo conductive electrodes, which effectively lowers the risk of faultwelding and simplifies the process of connection comparing to themechanically connection in the tightly pressing manner.

Please refer to FIG. 7C. FIG. 7C is a projection of a top view of an LEDfilament of the LED light bulb 20 c of FIG. 7A. As shown in FIG. 7C, inan embodiment, the LED filament may be curved to form a wave shaperesembling to a circle observed in a top view to surround the center ofthe light bulb or the stem. In different embodiments, the LED filamentobserved in the top view can form a quasi-circle or a quasi U shape.

As shown in FIG. 7B and FIG. 7C, the LED filament 100 surrounds with thewave shape resembling to a circle and has a quasi-symmetric structure inthe top view, and the lighting face of the LED filament 100 is alsosymmetric, e.g., the main lighting face Lm in the top view may facesoutwardly; therefore, the LED filament 100 may generate an effect of anomnidirectional light due to a symmetry characteristic with respect tothe quasi-symmetric structure of the LED filament 100 and thearrangement of the lighting face of the LED filament 100 in the topview. Whereby, the LED light bulb 20 c as a whole may generate an effectof an omnidirectional light close to a 360 degrees illumination.Additionally, the two joint points may be close to each other such thatthe conductive supports 51 a, 51 b are substantially below the LEDfilament 100. Visually, the conductive supports 51 a, 51 b keeps a lowprofile and is integrated with the LED filament 100 to show an elegancecurvature.

Please refer to FIG. 8A and FIG. 8B. FIG. 8A is a perspective view of anLED light bulb according to an embodiment of the present invention. FIG.8B is a front view (or a side view) of an LED light bulb of FIG. 8A. TheLED light bulb 20 d shown in FIG. 8A and FIG. 8B is analogous to the LEDlight bulb 20 c shown in FIG. 7A. As shown in FIG. 8A and FIG. 8B, theLED light bulb 20 d comprises a bulb shell 12, a bulb base 16 connectedto the bulb shell 12, two conductive supports 51 a, 51 b disposed in thebulb shell 12, supporting arms 15, a stem 19, and one single LEDfilament 100. The stem 19 comprises a stem bottom and a stem topopposite to each other. The stem bottom is connected to the bulb base16. The stem top extends to inside of the blub shell 12 (e.g., extendingto the center of the bulb shell 12) along an elongated direction of thestem 19. For example, the stem top may be substantially located at acenter of the inside of the bulb shell 12. In the embodiment, the stem19 comprises the stand 19 a. Herein the stand 19 a is deemed as a partof the whole stem 19 and thus the top of the stem 19 is the same as thetop of the stand 19 a. The two conductive supports 51 a, 51 b areconnected to the stem 19. The LED filament 100 comprises a filament bodyand two conductive electrodes 506. The two conductive electrodes 506 areat two opposite ends of the filament body. The filament body is the partof the LED filament 100 without the conductive electrodes 506. The twoconductive electrodes 506 are respectively connected to the twoconductive supports 51 a, 51 b. The filament body is around the stem 19.An end of the supporting arm 15 is connected to the stem 19 and anotherend of the supporting arm 15 is connected to the filament body.

Please refer to FIG. 8C. FIG. 8C is a top view of the LED light bulb 20d of FIG. 8A. As shown in FIG. 8B and FIG. 8C, the filament bodycomprises a main lighting face Lm and a subordinate lighting face Ls.Any portion of the main lighting face Lm is towards the bulb shell 12 orthe bulb base 16 at any angle, and any portion of the subordinatelighting face Ls is towards the stem 19 or towards the top of the stem19, i.e., the subordinate lighting face Ls is towards inside of the LEDlight bulb 20 d or towards the center of the bulb shell 12. In otherwords, when a user observes the LED light bulb 20 d from outside, theuser would see the main lighting face Lm of the LED filament 100 d atany angle. Based upon the configuration, the effect of illumination isbetter.

According to different embodiments, the LED filament 100 in differentLED light bulbs (e.g., the LED light bulb 20 c, or 20 d) may be formedwith different shapes or curves while all of the LED filaments 100 areconfigured to have symmetry characteristic. The symmetry characteristicis beneficial of creating an even, wide distribution of light rays, sothat the LED light bulb is capable of generating an omnidirectionallight effect. The symmetry characteristic of the LED filament 100 isdiscussed below.

The definition of the symmetry characteristic of the LED filament 100may be based on four quadrants defined in a top view of an LED lightbulb. The four quadrants may be defined in a top view of an LED lightbulb (e.g., the LED light bulb 20 c shown in FIG. 7A), and the origin ofthe four quadrants may be defined as a center of a stem/stand of the LEDlight bulb in the top view (e.g., a center of the top of the stand 19 ashown in FIG. 7A). The LED filament of the LED light bulb (e.g., the LEDfilaments 100 shown in FIG. 7A) in the top view may be presented as anannular structure, shape or, contour. The LED filament presented in thefour quadrants in the top view may be symmetric.

For example, the brightness presented by a portion of the LED filamentin the first quadrant in the top view is symmetric with that presentedby a portion of the LED filament in the second quadrant, in the thirdquadrant, or in the fourth quadrant in the top view while the LEDfilament operates. In some embodiments, the structure of a portion ofthe LED filament in the first quadrant in the top view is symmetric withthat of a portion of the LED filament in the second quadrant, in thethird quadrant, or in the fourth quadrant in the top view. In addition,an emitting direction of a portion of the LED filament in the firstquadrant in the top view is symmetric with that of a portion of the LEDfilament in the second quadrant, in the third quadrant, or in the fourthquadrant in the top view.

In another embodiment, an arrangement of LED chips in a portion of theLED filament in the first quadrant (e.g., a density variation of the LEDchips in the portion of the LED filament in the first quadrant) in thetop view is symmetric with an arrangement of LED chips in a portion ofthe LED filament in the second quadrant, in the third quadrant, or inthe fourth quadrant in the top view.

In another embodiment, a power configuration of LED chips with differentpower in a portion of the LED filament in the first quadrant in the topview is symmetric with a power configuration of LED chips with differentpower in a portion of the LED filament in the second quadrant, in thethird quadrant, or in the fourth quadrant in the top view.

In another embodiment, refractive indexes of segments of a portion ofthe LED filament in the first quadrant in the top view are symmetricwith refractive indexes of segments of a portion of the LED filament inthe second quadrant, in the third quadrant, or in the fourth quadrant inthe top view while the segments may be defined by distinct refractiveindexes.

In another embodiment, surface roughness of segments of a portion of theLED filament in the first quadrant in the top view are symmetric withsurface roughness of segments of a portion of the LED filament in thesecond quadrant, in the third quadrant, or in the fourth quadrant in thetop view while the segments may be defined by distinct surfaceroughness.

The LED filament presented in the four quadrants in the top view may bein point symmetry (e.g., being symmetric with the origin of the fourquadrants) or in line symmetry (e.g., being symmetric with one of thetwo axis the four quadrants).

A tolerance (a permissible error) of the symmetric structure of the LEDfilament in the four quadrants in the top view may be up to 20%-50%. Forexample, in a case that the structure of a portion of the LED filamentin the first quadrant is symmetric with that of a portion of the LEDfilament in the second quadrant, a designated point on portion of theLED filament in the first quadrant is defined as a first position, asymmetric point to the designated point on portion of the LED filamentin the second quadrant is defined as a second position, and the firstposition and the second position may be exactly symmetric or besymmetric with 20%-50% difference.

In addition, a length of a portion of the LED filament in one of thefour quadrants in the top view is substantially equal to that of aportion of the LED filament in another one of the four quadrants in thetop view. The lengths of portions of the LED filament in differentquadrants in the top view may also have 20%-50% difference.

The definition of the symmetry characteristic of the LED filament 100may be based on four quadrants defined in a side view, in a front view,or in a rear view of an LED light bulb. In the embodiments, the sideview may include a front view or a rear view of the LED light bulb. Thefour quadrants may be defined in a side view of an LED light bulb (e.g.,the LED light bulb 20 c shown in FIG. 7A). In such case, an elongateddirection of a stand (or a stem) from the bulb base 16 towards a top ofthe bulb shell 12 away from the bulb base 16 may be defined as theY-axis, and the X-axis may cross a middle of the stand (e.g., the stand19 a of the LED light bulb 20 c shown in FIG. 7A) while the origin ofthe four quadrants may be defined as the middle of the stand. Indifferent embodiment, the X-axis may cross the stand at any point, e.g.,the X-axis may cross the stand at the top of the stand, at the bottom ofthe stand, or at a point with a certain height (e.g., ⅔ height) of thestand.

In addition, portions of the LED filament presented in the firstquadrant and the second quadrant (the upper quadrants) in the side viewmay be symmetric (e.g., in line symmetry with the Y-axis) in brightness,and portions of the LED filament presented in the third quadrant and thefourth quadrant (the lower quadrants) in the side view may be symmetric(e.g., in line symmetry with the Y-axis) in brightness; however, thebrightness of the portions of the LED filament presented in the upperquadrants in the side view may be asymmetric with that of the portionsof the LED filament presented in the lower quadrants in the side view.

In some embodiments, portions of the LED filament presented in the firstquadrant and the second quadrant (the upper quadrants) in the side viewmay be symmetric (e.g., in line symmetry with the Y-axis) in structure;portions of the LED filament presented in the third quadrant and thefourth quadrant (the lower quadrants) in the side view may be symmetric(e.g., in line symmetry with the Y-axis) in structure. In addition, anemitting direction of a portion of the LED filament in the firstquadrant in the side view is symmetric with that of a portion of the LEDfilament in the second quadrant in the side view, and an emittingdirection of a portion of the LED filament in the third quadrant in theside view is symmetric with that of a portion of the LED filament in thefourth quadrant in the side view.

In another embodiment, an arrangement of LED chips in a portion of theLED filament in the first quadrant in the side view is symmetric with anarrangement of LED chips in a portion of the LED filament in the secondquadrant in the side view, and an arrangement of LED chips in a portionof the LED filament in the third quadrant in the side view is symmetricwith an arrangement of LED chips in a portion of the LED filament in thefourth quadrant in the side view.

In another embodiment, a power configuration of LED chips with differentpower in a portion of the LED filament in the first quadrant in the sideview is symmetric with a power configuration of LED chips with differentpower in a portion of the LED filament in the second quadrant in theside view, and a power configuration of LED chips with different powerin a portion of the LED filament in the third quadrant in the side viewis symmetric with a power configuration of LED chips with differentpower in a portion of the LED filament in the fourth quadrant in theside view.

In another embodiment, refractive indexes of segments of a portion ofthe LED filament in the first quadrant in the side view are symmetricwith refractive indexes of segments of a portion of the LED filament inthe second quadrant in the side view, and refractive indexes of segmentsof a portion of the LED filament in the third quadrant in the side vieware symmetric with refractive indexes of segments of a portion of theLED filament in the fourth quadrant in the side view while the segmentsmay be defined by distinct refractive indexes.

In another embodiment, surface roughness of segments of a portion of theLED filament in the first quadrant in the side view are symmetric withsurface roughness of segments of a portion of the LED filament in thesecond quadrant in the side view, and surface roughness of segments of aportion of the LED filament in the third quadrant in the side view aresymmetric with surface roughness of segments of a portion of the LEDfilament in the fourth quadrant in the side view while the segments maybe defined by distinct surface roughness.

Additionally, the portions of the LED filament presented in the upperquadrants in the side view may be asymmetric with the portions of theLED filament presented in the lower quadrants in the side view inbrightness. In some embodiments, the portion of the LED filamentpresented in the first quadrant and the fourth quadrant in the side viewis asymmetric in structure, in length, in emitting direction, inarrangement of LED chips, in power configuration of LED chips withdifferent power, in refractive index, or in surface roughness, and theportion of the LED filament presented in the second quadrant and thethird quadrant in the side view is asymmetric in structure, in length,in emitting direction, in arrangement of LED chips, in powerconfiguration of LED chips with different power, in refractive index, orin surface roughness. In order to fulfill the illumination purpose andthe requirement of omnidirectional lamps, light rays emitted from theupper quadrants (the portion away from the bulb base 16) in the sideview should be greater than those emitted from the lower quadrants (theportion close to the bulb base 16). Therefore, the asymmetriccharacteristic of the LED filament of the LED light bulb between theupper quadrants and the lower quadrants in the side view may contributeto the omnidirectional requirement by concentrating the light rays inthe upper quadrants.

A tolerance (a permissible error) of the symmetric structure of the LEDfilament in the first quadrant and the second quadrant in the side viewmay be 20%-50%. For example, a designated point on portion of the LEDfilament in the first quadrant is defined as a first position, asymmetric point to the designated point on portion of the LED filamentin the second quadrant is defined as a second position, and the firstposition and the second position may be exactly symmetric or besymmetric with 20%-50% difference.

In addition, a length of a portion of the LED filament in the firstquadrant in the side view is substantially equal to that of a portion ofthe LED filament in the second quadrant in the side view. A length of aportion of the LED filament in the third quadrant in the side view issubstantially equal to that of a portion of the LED filament in thefourth quadrant in the side view. However, the length of the portion ofthe LED filament in the first quadrant or the second quadrant in theside view is different from the length of the portion of the LEDfilament in the third quadrant or the fourth quadrant in the side view.In some embodiment, the length of the portion of the LED filament in thethird quadrant or the fourth quadrant in the side view may be less thanthat of the portion of the LED filament in the first quadrant or thesecond quadrant in the side view. The lengths of portions of the LEDfilament in the first and the second quadrants or in the third and thefourth quadrants in the side view may also have 20%-50% difference.

Please refer to FIG. 8D. FIG. 8D is the LED filament 100 shown in FIG.8B presented in two dimensional coordinate system defining fourquadrants. The LED filament 100 in FIG. 8D is the same as that in FIG.8B, which is a front view (or a side view) of the LED light bulb 20 dshown in FIG. 8A. As shown in FIG. 8B and FIG. 8D, the Y-axis is alignedwith the stand 19 a of the stem (i.e., being along the elongateddirection of the stand 19 a), and the X-axis crosses the stand 19 a(i.e., being perpendicular to the elongated direction of the stand 19a). As shown in FIG. 8D, the LED filament 100 in the side view can bedivided into a first portion 100 p 1, a second portion 100 p 2, a thirdportion 100 p 3, and a fourth portion 100 p 4 by the X-axis and theY-axis. The first portion 100 p 1 of the LED filament 100 is the portionpresented in the first quadrant in the side view. The second portion 100p 2 of the LED filament 100 is the portion presented in the secondquadrant in the side view. The third portion 100 p 3 of the LED filament100 is the portion presented in the third quadrant in the side view. Thefourth portion 100 p 4 of the LED filament 100 is the portion presentedin the fourth quadrant in the side view.

As shown in FIG. 8D, the LED filament 100 is in line symmetry. The LEDfilament 100 is symmetric with the Y-axis in the side view. That is tosay, the geometric shape of the first portion 100 p 1 and the fourthportion 100 p 4 are symmetric with that of the second portion 100 p 2and the third portion 100 p 3. Specifically, the first portion 100 p 1is symmetric to the second portion 100 p 2 in the side view.Particularly, the first portion 100 p 1 and the second portion 100 p 2are symmetric in structure in the side view with respect to the Y-axis.In addition, the third portion 100 p 3 is symmetric to the fourthportion 100 p 4 in the side view. Particularly, the third portion 100 p3 and the fourth portion 100 p 4 are symmetric in structure in the sideview with respect to the Y-axis.

In the embodiment, as shown in FIG. 8D, the first portion 100 p 1 andthe second portion 100 p 2 presented in the upper quadrants (i.e., thefirst quadrant and the second quadrant) in the side view are asymmetricwith the third portion 100 p 3 and the fourth portion 100 p 4 presentedin the lower quadrants (i.e., the third quadrant and the fourthquadrant) in the side view. In particular, the first portion 100 p 1 andthe fourth portion 100 p 4 in the side view are asymmetric, and thesecond portion 100 p 2 and the third portion 100 p 3 in the side vieware asymmetric. According to an asymmetry characteristic of thestructure of the filament 100 in the upper quadrants and the lowerquadrants in FIG. 8D, light rays emitted from the upper quadrants topass through the upper bulb shell 12 (the portion away from the bulbbase 16) would be greater than those emitted from the lower quadrants topass through the lower bulb shell 12 (the portion close to the bulb base16) in order to fulfill the illumination purpose and the requirement ofomnidirectional lamps.

Based upon symmetry characteristic of LED filament 100, the structuresof the two symmetric portions of the LED filament 100 in the side view(the first portion 100 p 1 and the second portion 100 p 2 or the thirdportion 100 p 3 and the fourth portion 100 p 4) may be exactly symmetricor be symmetric with a tolerance in structure. The tolerance (or apermissible error) between the structures of the two symmetric portionsof the LED filament 100 in the side view may be 20%-50% or less.

The tolerance can be defined as a difference in coordinates, i.e.,x-coordinate or y-coordinate. For example, if there is a designatedpoint on the first portion 100 p 1 of the LED filament 100 in the firstquadrant and a symmetric point on the second portion 100 p 2 of the LEDfilament 100 in the second quadrant symmetric to the designated pointwith respect to the Y-axis, the absolute value of y-coordinate or thex-coordinate of the designated point may be equal to the absolute valueof y-coordinate or the x-coordinate of the symmetric point or may have20% difference comparing to the absolute value of y-coordinate or thex-coordinate of the symmetric point.

For example, as shown in FIG. 8D, a designated point (x1, y1) on thefirst portion 100 p 1 of the LED filament 100 in the first quadrant isdefined as a first position, and a symmetric point (x2, y2) on thesecond portion 100 p 2 of the LED filament 100 in the second quadrant isdefined as a second position. The second position of the symmetric point(x2, y2) is symmetric to the first position of the designated point (x1,y1) with respect to the Y-axis. The first position and the secondposition may be exactly symmetric or be symmetric with 20%-50%difference. In the embodiment, the first portion 100 p 1 and the secondportion 100 p 2 are exactly symmetric in structure. In other words, x2of the symmetric point (x2, y2) is equal to negative x1 of thedesignated point (x1, y1), and y2 of the symmetric point (x2, y2) isequal to y1 of the designated point (x1, y1).

For example, as shown in FIG. 8D, a designated point (x3, y3) on thethird portion 100 p 3 of the LED filament 100 in the third quadrant isdefined as a third position, and a symmetric point (x4, y4) on thefourth portion 100 p 4 of the LED filament 100 in the fourth quadrant isdefined as a fourth position. The fourth position of the symmetric point(x4, y4) is symmetric to the third position of the designated point (x3,y3) with respect to the Y-axis. The third position and the fourthposition may be exactly symmetric or be symmetric with 20%-50%difference. In the embodiment, the third portion 100 p 3 and the fourthportion 100 p 4 are symmetric with a tolerance (e.g., a difference incoordinates being less than 20%) in structure. In other words, theabsolute value of x4 of the symmetric point (x4, y4) is unequal to theabsolute value of x3 of the designated point (x3, y3), and the absolutevalue of y4 of the symmetric point (x4, y4) is unequal to the absolutevalue of y3 of the designated point (x3, y3). As shown in FIG. 8D, thelevel of the designated point (x3, y3) is slightly lower than that ofthe symmetric point (x4, y4), and the designated point (x3, y3) isslightly closer to the Y-axis than the symmetric point (x4, y4) is.Accordingly, the absolute value of y4 is slightly less than that of y3,and the absolute value of x4 is slightly greater than that of x3.

As shown in FIG. 8D, a length of the first portion 100 p 1 of the LEDfilament 100 in the first quadrant in the side view is substantiallyequal to a length of the second portion 100 p 2 of the LED filament 100in the second quadrant in the side view. In the embodiment, the lengthis defined along an elongated direction of the LED filament 100 in aplane view (e.g., a side view, a front view, or a top view). Forexample, the first portion 100 p 1 elongates in the first quadrant inthe side view shown in FIG. 8D to form a reversed “V” shape with twoends respectively contacting the X-axis and the Y-axis, and the lengthof the first portion 100 p 1 is defined along the reversed “V” shapebetween the X-axis and the Y-axis.

In addition, a length of the third portion 100 p 3 of the LED filament100 in the third quadrant in the side view is substantially equal to alength of fourth portion 100 p 4 of the LED filament 100 in the fourthquadrant in the side view. Since the third portion 100 p 3 and thefourth portion 100 p 4 are symmetric with respect to the Y-axis with atolerance in structure, there may be a slightly difference between thelength of the third portion 100 p 3 and the length of fourth portion 100p 4. The difference may be 20%-50% or less.

As shown in FIG. 8D, an emitting direction of a designated point of thefirst portion 100 p 1 and an emitting direction of a symmetric point ofthe second portion 100 p 2 symmetric to the designated point aresymmetric in direction in the side view with respect to the Y-axis. Inthe embodiment, the emitting direction may be defined as a directiontowards which the LED chips face. Since the LED chips face the mainlighting face Lm, the emitting direction may also be defined as thenormal direction of the main lighting face Lm. For example, thedesignated point (x1, y1) of the first portion 100 p 1 has an emittingdirection ED which is upwardly in FIG. 8D, and the symmetric point (x2,y2) of the second portion 100 p 2 has an emitting direction ED which isupwardly in FIG. 8D. The emitting direction ED of the designated point(x1, y1) and the emitting direction ED of the symmetric point (x2, y2)are symmetric with respect to the Y-axis. In addition, the designatedpoint (x3, y3) of the third portion 100 p 3 has an emitting direction EDtowards a lower-left direction in FIG. 8D, and the symmetric point (x4,y4) of the fourth portion 100 p 4 has an emitting direction ED towards alower-right direction in FIG. 8D. The emitting direction ED of thedesignated point (x3, y3) and the emitting direction ED of the symmetricpoint (x4, y4) are symmetric with respect to the Y-axis.

Please refer to FIG. 8E. FIG. 8E is the LED filament 100 shown in FIG.8C presented in two dimensional coordinate system defining fourquadrants. The LED filament 100 in FIG. 8E is the same as that in FIG.8C, which is a top view of the LED light bulb 20 d shown in FIG. 8A. Asshown in FIG. 8C and FIG. 8E, the origin of the four quadrants isdefined as a center of a stand 19 a of the LED light bulb 20 d in thetop view (e.g., a center of the top of the stand 19 a shown in FIG. 8A).In the embodiment, the Y-axis is vertical, and the X-axis is horizontalin FIG. 8E. As shown in FIG. 8E, the LED filament 100 in the top viewcan be divided into a first portion 100 p 1, a second portion 100 p 2, athird portion 100 p 3, and a fourth portion 100 p 4 by the X-axis andthe Y-axis. The first portion 100 p 1 of the LED filament 100 is theportion presented in the first quadrant in the top view. The secondportion 100 p 2 of the LED filament 100 is the portion presented in thesecond quadrant in the top view. The third portion 100 p 3 of the LEDfilament 100 is the portion presented in the third quadrant in the topview. The fourth portion 100 p 4 of the LED filament 100 is the portionpresented in the fourth quadrant in the top view.

In some embodiments, the LED filament 100 in the top view may besymmetric in point symmetry (being symmetric with the origin of the fourquadrants) or in line symmetry (being symmetric with one of the two axisthe four quadrants). In the embodiment, as shown in FIG. 8E, the LEDfilament 100 in the top view is in line symmetry. In particular, the LEDfilament 100 in the top view is symmetric with the Y-axis. That is tosay, the geometric shape of the first portion 100 p 1 and the fourthportion 100 p 4 are symmetric with that of the second portion 100 p 2and the third portion 100 p 3. Specifically, the first portion 100 p 1is symmetric to the second portion 100 p 2 in the top view.Particularly, the first portion 100 p 1 and the second portion 100 p 2are symmetric in structure in the top view with respect to the Y-axis.In addition, the third portion 100 p 3 is symmetric to the fourthportion 100 p 4 in the top view. Particularly, the third portion 100 p 3and the fourth portion 100 p 4 are symmetric in structure in the topview with respect to the Y-axis.

Based upon symmetry characteristic of LED filament 100, the structuresof the two symmetric portions of the LED filament 100 in the top view(the first portion 100 p 1 and the second portion 100 p 2 or the thirdportion 100 p 3 and the fourth portion 100 p 4) may be exactly symmetricor be symmetric with a tolerance in structure. The tolerance (or apermissible error) between the structures of the two symmetric portionsof the LED filament 100 in the top view may be 20%-50% or less.

For example, as shown in FIG. 8E, a designated point (x1, y1) on thefirst portion 100 p 1 of the LED filament 100 in the first quadrant isdefined as a first position, and a symmetric point (x2, y2) on thesecond portion 100 p 2 of the LED filament 100 in the second quadrant isdefined as a second position. The second position of the symmetric point(x2, y2) is symmetric to the first position of the designated point (x1,y1) with respect to the Y-axis. The first position and the secondposition may be exactly symmetric or be symmetric with 20%-50%difference. In the embodiment, the first portion 100 p 1 and the secondportion 100 p 2 are exactly symmetric in structure. In other words, x2of the symmetric point (x2, y2) is equal to negative x1 of thedesignated point (x1, y1), and y2 of the symmetric point (x2, y2) isequal to y1 of the designated point (x1, y1).

For example, as shown in FIG. 8E, a designated point (x3, y3) on thethird portion 100 p 3 of the LED filament 100 in the third quadrant isdefined as a third position, and a symmetric point (x4, y4) on thefourth portion 100 p 4 of the LED filament 100 in the fourth quadrant isdefined as a fourth position. The fourth position of the symmetric point(x4, y4) is symmetric to the third position of the designated point (x3,y3) with respect to the Y-axis. The third position and the fourthposition may be exactly symmetric or be symmetric with 20%-50%difference. In the embodiment, the third portion 100 p 3 and the fourthportion 100 p 4 are symmetric with a tolerance (e.g., a difference incoordinates being less than 20%) in structure. In other words, x4 of thesymmetric point (x4, y4) is unequal to negative x3 of the designatedpoint (x3, y3), and y4 of the symmetric point (x4, y4) is unequal to y3of the designated point (x3, y3). As shown in FIG. 8E, the level of thedesignated point (x3, y3) is slightly lower than that of the symmetricpoint (x4, y4), and the designated point (x3, y3) is slightly closer tothe Y-axis than the symmetric point (x4, y4) is. Accordingly, theabsolute value of y4 is slightly less than that of y3, and the absolutevalue of x4 is slightly greater than that of x3.

As shown in FIG. 8E, a length of the first portion 100 p 1 of the LEDfilament 100 in the first quadrant in the top view is substantiallyequal to a length of the second portion 100 p 2 of the LED filament 100in the second quadrant in the top view. In the embodiment, the length isdefined along an elongated direction of the LED filament 100 in a planeview (e.g., a top view, a front view, or a top view). For example, thesecond portion 100 p 2 elongates in the second quadrant in the top viewshown in FIG. 8E to form a reversed “L” shape with two ends respectivelycontacting the X-axis and the Y-axis, and the length of the secondportion 100 p 2 is defined along the reversed “L” shape.

In addition, a length of the third portion 100 p 3 of the LED filament100 in the third quadrant in the top view is substantially equal to alength of fourth portion 100 p 4 of the LED filament 100 in the fourthquadrant in the top view. Since the third portion 100 p 3 and the fourthportion 100 p 4 are symmetric with respect to the Y-axis with atolerance in structure, there may be a slightly difference between thelength of the third portion 100 p 3 and the length of fourth portion 100p 4. The difference may be 20%-50% or less.

As shown in FIG. 8E, an emitting direction of a designated point of thefirst portion 100 p 1 and an emitting direction of a symmetric point ofthe second portion 100 p 2 symmetric to the designated point aresymmetric in direction in the top view with respect to the Y-axis. Inthe embodiment, the emitting direction may be defined as a directiontowards which the LED chips face. Since the LED chips face the mainlighting face Lm, the emitting direction may also be defined as thenormal direction of the main lighting face Lm. For example, thedesignated point (x1, y1) of the first portion 100 p 1 has an emittingdirection ED towards right in FIG. 8E, and the symmetric point (x2, y2)of the second portion 100 p 2 has an emitting direction ED towards leftin FIG. 8E. The emitting direction ED of the designated point (x1, y1)and the emitting direction ED of the symmetric point (x2, y2) aresymmetric with respect to the Y-axis. In addition, the designated point(x3, y3) of the third portion 100 p 3 has an emitting direction EDtowards a lower-left direction in FIG. 8E, and the symmetric point (x4,y4) of the fourth portion 100 p 4 has an emitting direction ED towards alower-right direction in FIG. 8E. The emitting direction ED of thedesignated point (x3, y3) and the emitting direction ED of the symmetricpoint (x4, y4) are symmetric with respect to the Y-axis. In addition, anemitting direction ED of any designated point of the first portion 100 p1 and an emitting direction ED of a corresponding symmetric point of thesecond portion 100 p 2 symmetric to the designated point are symmetricin direction in the top view with respect to the Y-axis. An emittingdirection ED of any designated point of the third portion 100 p 3 and anemitting direction ED of a corresponding symmetric point of the fourthportion 100 p 4 symmetric to the designated point are symmetric indirection in the top view with respect to the Y-axis.

Definition of the omni-directional light depends on regions and variesover time. Depending on different institutions and countries, LED lightbulbs which claim omni-directional light may need to meet differentstandards. For example, page 24 of the ENERGY STAR Program Requirementsfor Lamps (bulbs)—Eligibility Criteria Version 1.0 defines that anomnidirectional lamp in base-on position has to emit at least 5% oftotal flux (Im) in 135° to 180° zone, that 90% of measured intensityvalues may vary by no more than 25% from the average of all measuredvalues in all planes, and that luminous intensity (cd) is measuredwithin each vertical plane at a 5° vertical angle increment (maximum)from 0° to 135°. Japanese JEL 801 requires luminous flux of an LED lampwithin a 120 degrees zone about a light axis shall not be less than 70%of total flux. Because the above embodiment possesses a symmetricalarrangement of LED filament, an LED light bulb with the LED filament isable to meet various standards of omni-directional lamps.

Referring to FIGS. 9A to 9D, FIG. 9A is a perspective diagram of an LEDlight bulb 40 b according to an embodiment of the present invention, andFIGS. 9B to 9D are respectively side views, another side view, and topview of the FIG. 9A. In the present embodiment, the LED light bulb 40 bincludes a lamp housing 12, a bulb base 16 connected to the lamp housing12, a stem 19, a stand 19 a, and a single LED filament 100. The LEDfilament 100 includes two conductive electrodes 110, 112 disposed at twoends, a plurality of LED sections 102, 104 and a plurality of the firstand second conductive sections 130, 130′. Moreover, the LED light bulb40 b and the LED filament 100 disposed in the LED light bulb 40 b mayrefer to related descriptions of the previous embodiments, wherein thesame or similar components and the connection relationship betweencomponents is no longer detailed.

As shown in FIG. 9A to FIG. 9D, the LED filament 100 comprises threefirst conductive sections 130, two second conductive sections 130′ of,and six LED sections 102, 104, and every two adjacent LED sections 102,104 are connected through the bending first or second conductivesections 130, 130′. Therefore, a single LED filament 100 in the LEDlight bulb 40 b can be bent severer because of the first and secondconductive sections 130, 130′, and the curling modification in bendingis more significant. Moreover, the LED filament 100 can be defined ashaving a plurality of sections, each of the sections is connectedbetween the first and second conductive sections 130, 130′, and each LEDsection 102, 104 is formed into a respective section. In the presentembodiment, the LED filament 100 is bent into six sections by the threefirst conductive sections 130 and the two second conductive sections130′, wherein the six LED sections 102, 104 are respectively the sixpieces.

Referring to FIG. 9A and FIG. 9B, in the present embodiment, the heightof the upper three first conductive sections 130 may be greater than theheight of the other lower two second conductive sections 130′ in the Zdirection. The height of the four LED sections 102, 104 is between theupper first conductive section 130 and the lower second conductivesection 130′ in the Z direction. The other two LED sections 102, 104extend downward from the corresponding first conductive section 130 inthe Z direction, and the height of the conductive electrodes 110, 112 isless than the height of the first conductive section 130 in the Zdirection. As shown in FIG. 9C of the present embodiment, theprojections of the opposite LED sections 102, 104 are overlapped eachother when the LED filament 100 is projected on the XZ plane. In theembodiment as shown in FIG. 9D, when the LED filament 100 is projectedon the XY plane, the projections of all the second conductive sections130′ are located in one side of a straight line connecting between theconductive electrodes 110, 112, and the projections of the firstconductive section 130 is dispersed on both sides of the straight lineconnecting between the conductive electrodes 110, 112.

Referring to FIG. 10, which is a schematic diagram of the light emissionspectrum of an LED light bulb according to an embodiment of the presentinvention. In the present embodiment, the LED light bulb may be any ofthe LED light bulbs disclosed in the previous embodiments, and any oneof the LED light bulbs disclosed in the previous embodiments isprovided. The light emitted by the LED light bulb is measured by aspectrometer to obtain a spectrum diagram as shown in FIG. 10. From thespectrum diagram, the spectral distribution of the LED light bulb ismainly between the wavelength ranges of about 400 nm to 800 nm.Moreover, there are three peaks of intensity values P1, P2, P3 inwavelength ranges corresponding to the light emitted by the LED lightbulb. The wavelength of the intensity value P1 is between about 430 nmand 480 nm, the wavelength of the intensity value P2 is between about580 nm and 620 nm, and the wavelength of the intensity value P3 isbetween about 680 nm and 750 nm. The light intensity of the peak P1 isless than that of the peak P2, and the light intensity of the peak P2 isless than the light intensity of the peak P3. As shown in FIG. 10, sucha spectral distribution is close to the spectral distribution of aconventional incandescent filament lamp and also close to the spectraldistribution of natural light. In accordance with an embodiment of thepresent invention, a schematic diagram of the light emission spectrum ofa single LED filament is shown in FIG. 11. From the spectrum diagram, itcan be seen that the spectral distribution of the LED light bulb ismainly between the wavelength range of about 400 nm to 800 nm, and thereare three peaks of intensity values P1, P2, P3 in that wavelength range.The wavelength of the intensity value P1 is between about 430 nm and 480nm, the wavelength of the intensity value P2 is between about 480 nm and530 nm, and the wavelength of the intensity value peak P3 is betweenabout 630 nm and 680 nm. Such a spectral distribution is close to thespectral distribution of a conventional incandescent filament lamp andalso close to the spectral distribution of natural light.

The meaning of the term “a single LED filament” and “a single strip LEDfilament” as used in the present invention is mainly composed of theaforementioned conductive section, the LED section, the connectionbetween thereof, the light conversion layer (including the consecutivetop layer or the bottom layer, with continuous formation to cover orsupport all the components), and two conductive electrodes electricallyconnected to the conductive brackets of the LED light bulb disposing atboth ends of the LED filament, which is the single LED filamentstructure referred to in the present invention.

In some embodiments, LED filament 100 may have multiple LED sections. Atleast part or all of LED chips on a single LED section are electricallyconnected in series. Different LED sections are electrically connectedin parallel. Anode and cathode of each LED section may serve as apositive electrode and negative electrodes of the LED filament,respectively. The negative electrodes separately connect with two ormore of the conductive supports (e.g., conductive supports 51 a, 51 b inFIG. 7A) and finally connect to a power module (such as power module 518in FIG. 7A). As shown in FIG. 12A, which is a schematic circuit diagramof the LED filament according to some embodiments of the presentinvention, LED filament 100 in this embodiment has two LED sections 402,404. Each LED section 402, 404 includes one or more LED chips. LED chipsin a single LED section are electrically connected in series. Two LEDsections 402, 404 have respective current paths after they have beenelectrically electrically connected (i.e. in parallel). In detail, inthis embodiment, anodes of LED sections 402, 404 are electricallyconnected together to serve as a positive electrode P1 of LED filament100. Cathodes of LED section 402 and 404 serve as a first negativeelectrode N1 and a second negative electrode N2, respectively. Positiveelectrode P1, first negative electrode N1 and second negative electrodeN2 are separately electrically connected to the power module throughconductive supports such as conductive supports 51 a, 51 b and powermodule 518 shown in FIG. 7A.

In more detail, the connection relationship between positive electrodeP1, first negative electrode N1 and second negative electrode N2 may beshown as FIG. 12B or FIG. 12C, in which FIGS. 12B and 12C are twoschematic views of electrical connections of the LED filament accordingto some embodiments of the present invention. Please refer to FIG. 12Bfirst. In this embodiment, positive electrode P1 of LED filament 100 iselectrically connected to a first output terminal (also called “positiveoutput terminal) of power module 518. First and second negativeelectrodes N1, N2 of LED filament 100 are electrically connectedtogether and then jointly electrically connected to a second outputterminal (also called “negative output terminal”) of power module 518.Further refer to FIG. 12A, under the electrical relationship shown inFIG. 12B, LED sections 402, 404 can be deemed as being electricallyconnected to the output terminals of power module 518 in parallel. Thus,all LED sections 402, 404 are driven by driving voltage V1 between thefirst and second output terminals. Under a precondition of LED sections402, 404 having identical or similar chips number and arrangement, thedriving current from power module 518 will evenly dividedly flow to eachof LED sections 402, 404. As a result, LED sections 402, 404 can presentapproximately even intensity and/or color temperature.

Please further refer to FIG. 12C. In this embodiment, positive electrodeP1 of LED filament 100 is electrically connected to the first outputterminal of power module 518, first negative electrode N1 of LEDfilament 100 is electrically connected to the second output terminal(also called “first negative output terminal”) of power module 518, andthe second negative electrode N2 of LED filament 100 is electricallyconnected to the third output terminal (also called “second negativeoutput terminal”) of power module 518. Driving voltage V1 is formedbetween the first output terminal and the second output terminal ofpower module 518, and another driving voltage V2 is formed between thefirst output terminal and the third output terminal of power module 518.Referring to FIG. 12A together, under the electrical relationship shownin FIG. 12C, LED section 402 is electrically connected between the firstoutput terminal and the second output terminal, and LED section 404 iselectrically connected between the first output terminal and the thirdoutput terminal. As a result, LED sections 402 and 404 can be deemed asbeing driven by driving voltages V1, and V2, respectively. In such anarrangement, the driving currents provided by power module 518 to LEDsections 402, 404 can be independently controlled by adjusting outputvoltages V1 and V2, so as to make LED sections 402, 404 separatelygenerate corresponding intensity and/or color temperature. In otherwords, dimming the different LED sections individually on a single LEDfilament can be implemented by design and control of the power modulebased on the arrangement of FIG. 12C.

In some embodiments, the second and third output terminals of powermodule 518 can be electrically connected together through a resistor,and either of the second and third output terminals of the power module518 is electrically connected to a ground terminal. By this arrangement,negative output terminals with different levels can be obtained togenerate two different driving voltages V1 and V2. In some embodiments,levels of the second and third output terminals can be controlled by acircuit. The present invention is not limited thereto.

The invention has been described above in terms of the embodiments, andit should be understood by those skilled in the art that the presentinvention is not intended to limit the scope of the invention. It shouldbe noted that variations and permutations equivalent to those of theembodiments are intended to be within the scope of the presentinvention. Therefore, the scope of the invention is defined by the scopeof the appended claims.

What is claimed is:
 1. An LED light bulb, consisting of: a lamp housingdoped with a golden yellow material and its surface coated with a yellowfilm; a bulb base connected to the lamp housing; a stem connected to thebulb base and located in the lamp housing, the stem comprises a standextending to the center of the lamp housing; a single flexible LEDfilament, disposed in the lamp housing, and the flexible LED filamentcomprising; a plurality of LED sections, each of the LED sectionsincludes at least two LED chips that are electrically connected to eachother by a wire; a plurality of conductive sections comprising aconductor, located between the adjacent two LED sections; two conductiveelectrodes, disposed corresponding to the LED sections and electricallyconnected to the LED sections; a light coversion layer disposing on theLED chip and at least two sides of the conductive electrodes andexposing a portion of the conductive electrodes, the light coversionlayer is composed of at least one top layer and at least one base layer,wherein the top layer only covers the LED chip and the conductorcompletely and exposes a portion of the wire; a plurality of supportingarms, each of the supporting arms comprising a first end and a secondend opposite to the first end of the supporting arms, the first end ofeach of the supporting arms is connected with the stand while the secondend of each of the supporting arms is connected with the flexible LEDfilament; two conductive supports, disposed in the lamp housing andconnected with both the stem and the flexible LED filament; and adriving circuit, electrically connected with two conductive supports;wherein the base layer of the light conversion layer is formed fromorganosilicon-modified polyimide resin composition comprising anorganosilicon-modified polyimide and a thermal curing agent, wherein theorganosilicon-modified polyimide comprises a repeating unit representedby the following general Formula (I):

wherein Ar¹ is a tetra-valent organic group having a benzene ring or analicyclic hydrocarbon structure, Are is a di-valent organic group havinga monocyclic alicyclic hydrocarbon structure, R is each independentlymethyl or phenyl, n is 1˜5; wherein the organosilicon-modified polyimidehas a number average molecular weight of 5000˜100000; and wherein thethermal curing agent is selected from the group consisting of epoxyresin, isocyanate and bisoxazoline compounds.
 2. The LED light bulbaccording to claim 1, wherein the shortest distance between the two LEDchips located in the adjacent two LED section is greater than thedistance between adjacent two LED chips in one LED section.
 3. The LEDlight bulb according to claim 2, wherein one of six faces of the LEDchip farthest from the base layer is defined as the upper surface of theLED chip, the distance from the upper surface of the LED chip to thesurface of top layer is in a range of 100 to 200 μm.
 4. The LED lightbulb according to claim 3, wherein the length of the wire is less thanthat of conductor.
 5. The LED light bulb according to claim 4, whereinthe light emitted by the LED chip passes through interfaces A, B, C, D,E and F respectively in the light bulb, where the interface A is theinterface between p-GaN gate of the LED chip and the top layer of thelight conversion layer, the interface B is the interface between the toplayer of the light conversion layer and the gas in the bulb shell, theinterface C is the interface between Base of the LED chip and pasteadjacent to the base layer of the light conversion layer, the interfaceD is the interface between the paste and the base layer of the lightconversion layer, the interface E is the interface between the baselayer of the light conversion layer and the gas in the bulb shell, andthe interface F is the interface between the base layer of the lightconversion layer and the top layer of the light conversion layer, andthe absolute value of the refractive index difference between the twosubstances in any interface is less than 1.0.
 6. The LED light bulbaccording to claim 5, wherein the absolute value of the refractive indexdifference between the two substances in any one of the two interfacesof D and F is less than 0.5.
 7. The LED light bulb according to claim 6,wherein the absolute value of the refractive index difference betweenthe two substances in any one of the two interfaces of D and F is lessthan 0.2.
 8. The LED light bulb according to claim 7, wherein Ar¹ is atetra-valent organic group having a monocyclic alicyclic hydrocarbonstructure or a bridged-ring alicyclic hydrocarbon structure.
 9. The LEDlight bulb according to claim 8, wherein Ar² is a di-valent organicgroup comprising a functional group having active hydrogen, where thefunctional group having active hydrogen is any one of hydroxyl, amino,carboxy and mercapto.
 10. The LED light bulb according to claim 9,wherein Ar¹ is derived from a dianhydride, and Ar² is derived from adiamine.
 11. The LED light bulb according to claim 10, wherein siloxanecontent in the organosilicon-modified polyimide is 30˜70 wt %, and theorganosilicon-modified polyimide has a glass transition temperature ofbelow 150° C.
 12. The LED light bulb according to claim 11, wherein theorganosilicon-modified polyimide resin composition further comprises anadditive selected from the group consisting of fluorescent powders, heatdispersing particles and a coupling agent.
 13. The LED light bulbaccording to claim 12, wherein the base layer comprise an upper surfacewhere the LED chips is positioned and a lower surface opposite to theupper surface of the base layer, the lower surface of the base layer hasa third area and a fourth area, where the surface roughness of the thirdarea of the lower surface is higher than that of the fourth area with acell.
 14. The LED light bulb according to claim 13, wherein the surfaceroughness of the upper surface of the base layer is equal to the fourtharea of the lower surface.
 15. The LED light bulb according to claim 14,wherein the base layer has an elastic modulus of more than 2.0 GPa, andan elongation at break of more than 0.5%.
 16. The LED light bulbaccording to claim 15, wherein a spectral distribution of the light bulbis between wavelength range of about 400 nm to 800 nm, and three peakwavelengths P1, P2, P3 are appeared in the wavelength rangescorresponding to light emitted by the light bulb, the wavelength of thepeak P1 is between 430 nm and 480 nm, the wavelength of the peak P2 isbetween 580 nm and 620 nm, and the wavelength of the peak P3 is between680 nm and 750 nm, wherein a light intensity of the peak P1 is less thanthat of the peak P2, and the light intensity of the peak P2 is less thanthat of the peak P3.
 17. The LED light bulb according to claim 16,wherein points of the flexible LED filament in an xyz coordinates aredefined as X, Y, Z, an x-y plane of the xyz coordinates is perpendicularto the height direction of the light bulb, a z-axis of xyz coordinatesis parallel with the stem, where the conductive sections comprise threefirst conductive sections and two second conductive sections, and eachof the LED sections is connected between the first conductive sectionand the second conductive section.
 18. The LED light bulb according toclaim 17, wherein the height of the first conductive section is greaterthan that of the second conductive section in the Z direction.
 19. TheLED light bulb according to claim 18, wherein the number of theconductive sections is one less than that of the LED sections.
 20. TheLED light bulb according to claim 19, wherein the projections of all thesecond conductive sections are located in one side of a straight lineconnecting between the two conductive electrodes and the projections ofthe first conductive sections is dispersed on both sides of the straightline connecting between the two conductive electrodes on the XZ plane.